Chapter 21:
Masonry
General Comments
Masonry construction has been used for at least 10,000
years in a variety of structures—homes, private and public buildings and historical monuments. The masonry of
ancient times involved two major materials: brick manufactured from sun-dried mud or burned clay and shale;
and natural stone.
The first masonry structures were unreinforced and intended to support mainly gravity loads. The weight of
these structures stabilized them against lateral loads from
wind and earthquakes.
Masonry construction has progressed through several
stages of development. Fired clay brick became the principal building material in the United States during the middle 1800s. Concrete masonry was introduced to
construction during the early 1900s and, along with clay
masonry, expanded in use to all types of structures.
Historically, “rules of thumb” (now termed “empirical design”) were the only available methods of masonry design. Only in recent times have masonry structures been
engineered using structural calculations. In the last 45
years, the introduction of engineered reinforced masonry
has resulted in structures that are stronger and more stable against lateral loads, such as wind and seismic.
Masonry consists of a variety of materials. Raw materials are made into masonry units of different sizes and
shapes, each having specific physical and mechanical
properties. Both the raw materials and the method of
manufacture affect masonry unit properties.
The word “masonry” is a general term that applies to
construction using hand-placed units of clay, concrete,
structural clay tile, glass block, natural stones and the like.
One or more types of masonry units are bonded together
with mortar, metal ties, reinforcement and accessories to
form walls and other structural elements.
Proper masonry construction depends on correct design, materials, handling, installation and workmanship.
With a fundamental understanding of the functions and
properties of the materials that comprise masonry construction and with proper design and construction, quality
masonry structures are not difficult to obtain.
During the pioneer era of U.S. history, the fireplace was
the central focus of residential cooking and heating. To-
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
day, the fireplace is essentially a decorative feature of residential construction. For energy conservation, existing
fireplaces are sometimes converted and new fireplaces
are designed to provide supplemental heat.
Of the many types of fireplaces, the most common are
single face. Multifaced fireplaces, such as a corner fireplace with two adjacent open sides, fireplaces with two
opposite faces open (common exposure to two rooms) or
fireplaces with three or all faces open also occur, but are
less common.
While the provisions of this chapter are for single-faced
fireplaces, almost all types of masonry fireplaces include
the same basic construction features: the base assembly,
which consists of a foundation and hearth support; the
firebox assembly, which consists of a fireplace opening, a
hearth, a firebox or combustion chamber and the throat
and the smoke chamber, which supports the chimney
liner.
Masonry fireplaces are made primarily of clay brick or
natural stones, but also of concrete masonry or
cast-in-place concrete. Chimneys for medium- and
high-heat appliances require special attention for fire
safety.
Purpose
Chapter 21 provides comprehensive and practical requirements for masonry construction, based on the latest
state of technical knowledge. The provisions of Chapter
21 require minimum accepted practices and the use of
standards for the design and construction of masonry
structures and elements of structures. The provisions address: material specifications and test methods; types of
wall construction; criteria for engineered design (by working stress and strength design methods); criteria for empirical design; required details of construction and other
aspects of masonry, including execution of construction.
The provisions are intended to result in safe and durable
masonry. The provisions of Chapter 21 are also intended
to prescribe minimum accepted practices for the design
and construction of glass unit masonry, masonry fireplaces, masonry heaters and masonry chimneys.
21-1
2101 – 2101.2.1
MASONRY
SECTION 2101
GENERAL
2101.1 Scope. This chapter shall govern the materials, design,
construction and quality of masonry.
v Section 2101 prescribes general requirements for masonry designed in accordance with Chapter 21 of the
code. It identifies masonry design methods and the conditions required for the use of each method. The methods
are intended as a practical means for safety under a variety of potential service conditions.
Minimum requirements for construction documents and
fireplace drawings are also included in Section 2101.
Chapter 21 contains the minimum code requirements
for acceptance of masonry design and construction by the
building official. Compliance with these requirements is intended to result in masonry construction with the minimum
required structural adequacy and durability. Requirements
more stringent than these are appropriate where mandated by sound engineering and judgement. Less restrictive requirements, however, are not permitted.
2101.2 Design methods. Masonry shall comply with the provisions of one of the following design methods in this chapter as
well as the requirements of Sections 2101 through 2104. Masonry designed by the working stress design provisions of Section 2101.2.1, the strength design provisions of Section
2101.2.2 or the prestressed masonry provisions of Section
2101.2.3 shall comply with Section 2105.
v This section requires masonry to comply with one of six
design methods and the requirements contained in
Sections 2101 through 2104 for construction documents, materials and construction.
The six design methods listed in Sections 2101.2.1
through 2101.2.6 can be categorized into two general
design approaches for masonry. The first approach, engineered design, encompasses working stress, prestressed masonry and strength design. Use of these design methods necessitates a quality assurance program
in accordance with Section 2105. The second approach, prescriptive design, includes the empirical design method, provisions for glass unit masonry and provisions for masonry veneer. Prescriptive design is
permitted only under limited conditions as noted in Section 2109.1.1.
When the design professional chooses engineered
design, the prescriptive masonry requirements of this
chapter do not apply. For example, Section 2109 does
not apply to engineered masonry.
Other provisions of the code also apply to masonry.
For example, fire-resistant construction using masonry
is required to comply with Chapter 7. Design loads and
related requirements, including seismic forces and detailing, are required to comply with Chapter 16. Masonry
foundations are required to comply with the provisions
21-2
of Chapter 18. Special inspections of masonry construction are required in Chapter 17. Masonry veneer is
addressed in Chapter 14.
2101.2.1 Working stress design. Masonry designed by the
working stress design method shall comply with the provisions
of Sections 2106 and 2107.
v This section requires that masonry designed by the
working stress design method meets both the working
stress design requirements in Section 2107 and the
seismic design requirements in Section 2106. Section
2107 requires working stress design to comply with
Chapters 1 and 2 of ACI 530/ASCE 5/TMS 402 with minor exceptions. Additional information on these procedures is given in the commentaries to Section 2107 and
ACI 530/ASCE 5/TMS 402.
ACI 530/ASCE 5/TMS 402 and ACI 530.1/ASCE
6/TMS 602 are referenced throughout Chapter 21. A
description of these standards is warranted here. Both
are joint publications of the American Concrete Institute
(ACI), the Structural Engineering Institute of the American Society of Civil Engineers (ASCE) and The Masonry Society (TMS) and are produced through a joint
committee of those societies, called the Masonry Standards Joint Committee (MSJC). These standards are
typically referred to as the MSJC Code and Specification to reflect their joint authorship and sponsorship of
the committee that oversees their development. The
standards are developed through an ANSI-regulated
consensus process and reflect the current state of technical knowledge on masonry design and construction.
The MSJC Code (ACI 530/ASCE 5/TMS 402) contains minimum requirements for masonry elements of
structures. Topics include: construction documents;
quality assurance; materials; analysis and design;
strength and serviceability; flexural and axial stresses;
shear; reinforcement; walls; columns; pilasters; beams
and lintels and empirical design.
The engineered method in ACI 530/ASCE 5/TMS 402
is a working stress design method, which assumes linearly elastic material behavior and properties and uses
working loads (see Chapter 16). The strength design
method is also specified in the standard.
The MSJC Specification (ACI 530.1/ASCE 6/TMS 602)
sets minimum acceptable levels of construction. It includes minimum requirements for composition; preparation and placement of materials; quality assurance for materials and masonry; execution of masonry construction;
inspection and verification of quality. ACI 530.1/ASCE
6/TMS 602 contains both mandatory and optional requirements. The mandatory requirements are enforceable
code requirements; the optional requirements may be invoked by the design professional. The specification is
meant to be modified for use with the particular project under design.
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MASONRY
2101.2.2 Strength design. Masonry designed by the strength
design method shall comply with the provisions of Sections
2106 and 2108.
v Masonry is required to meet the strength design provisions referenced in Section 2108 and the seismic design requirements in Section 2106.
2101.2.3 Prestressed masonry. Prestressed masonry shall be
designed in accordance with Chapters 1 and 4 of ACI
530/ASCE 5/TMS 402 and Section 2106. Special inspection
during construction shall be provided as set forth in Section
1704.5.
v Prestressed masonry must comply with the applicable
chapters of the ACI referenced standard, Building Code
Requirements for Masonry Structures. Additional requirements for prestressed masonry shear walls used
to resist earthquake loads are found in Section 2106.
2101.2.4 Empirical design. Masonry designed by the empirical
design method shall comply with the provisions of Sections
2106 and 2109 or Chapter 5 of ACI 530/ASCE 5/TMS 402.
v This section permits the empirical design of masonry either by the provisions of Sections 2106 and 2109, or
Chapter 5 of ACI 530/ASCE 5/TMS 402. This is because nearly all of the requirements in Section 2109 are
based on the requirements in Chapter 5 of ACI
530/ASCE 5/TMS 402. Additional information on these
provisions is given in the commentaries to Section 2109
and ACI 530/ASCE 5/TMS 402.
2101.2.5 Glass masonry. Glass masonry shall comply with the
provisions of Section 2110 or with the requirements of Chapter
7 of ACI 530/ASCE 5/TMS 402.
v Glass masonry must comply with either the provisions of
Section 2110 or Chapter 7 of ACI 530/ASCE 5/TMS 402.
The provisions in Section 2110 are based on the requirements in Chapter 7 of ACI 530/ASCE 5/TMS 402. Additional information on these provisions is given in the commentaries to Section 2109 and ACI 530/ASCE 5/TMS
402.
2101.2.6 Masonry veneer. Masonry veneer shall comply with
the provisions of Chapter 14.
v This section requires masonry veneer to comply with
the provisions of Chapter 14; specifically, Sections
1405.5 for anchored masonry veneer and 1405.9 for adhered masonry veneer. These sections reference the
provisions in Chapter 6 of ACI 530/ASCE 5/TMS 402.
Additional information on these provisions is given in
the commentaries to Chapter 14 and ACI 530/ASCE
5/TMS 402.
2101.3 Construction documents. The construction documents
shall show all of the items required by this code including the
following:
1. Specified size, grade, type and location of reinforcement,
anchors and wall ties.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2101.2.2 – 2102.1
2. Reinforcing bars to be welded and welding procedure.
3. Size and location of structural elements.
4. Provisions for dimensional changes resulting from elastic
deformation, creep, shrinkage, temperature and moisture.
v Construction requirements must be clearly identified in
the contract documents so that the structure is properly
constructed using appropriate materials and methods.
This section requires that, as a minimum, critical items
required by the code and by the particular design be
shown in the construction documents. The list is a minimum and should not be considered all-inclusive by the
design professional. Both the design professional and
the building official are permitted to require additional
items as needed for a particular structure.
2101.3.1 Fireplace drawings. The construction documents
shall describe in sufficient detail the location, size and construction of masonry fireplaces. The thickness and characteristics of
materials and the clearances from walls, partitions and ceilings
shall be clearly indicated.
v This section requires the submission of construction
documents for all fireplaces so that compliance with appropriate code sections can be properly determined
during plan review. The type of information and its format for plan review are established in this section. Construction documents are required showing relationships
of components, as well as details related to the specific
characteristics of the materials and techniques to be
used when erecting the fireplace and chimney system.
Such details are to include the type of brick or stone; refractory brick; concrete masonry; mortar requirements;
wall thicknesses; clearances; dimensions of openings
and dimensions of the firebox and the hearth extension.
SECTION 2102
DEFINITIONS AND NOTATIONS
2102.1 General. The following words and terms shall, for the
purposes of this chapter and as used elsewhere in this code, have
the meanings shown herein.
v This section contains definitions of terms associated
with the subject matter of this chapter. Definitions of
terms can help in the understanding and application of
code requirements. Definitions are included within this
chapter to provide convenient access to them without
having to refer back to Chapter 2.
ADOBE CONSTRUCTION. Construction in which the exterior load-bearing and nonload-bearing walls and partitions are
of unfired clay masonry units, and floors, roofs and interior
framing are wholly or partly of wood or other approved materials.
Adobe, stabilized. Unfired clay masonry units to which admixtures, such as emulsified asphalt, are added during the
manufacturing process to limit the units’ water absorption so
as to increase their durability.
21-3
FIGURE 2102.1(1)
MASONRY
Adobe, unstabilized. Unfired clay masonry units that do not
meet the definition of “Adobe, stabilized.”
v Adobe masonry was popular in the southwest United
States due to the availability of soil for units, the frequent exposure to intense sunlight to dry the units, the
thermal mass provided by the completed adobe structure and the low cost of this form of construction. This
form of construction has relatively low strength, a lack of
formalized design procedures and labor-intensive manufacture of units and construction of the building, and
accordingly, has not been used as much in recent years.
The two types of adobe masonry, stabilized and
unstabilized, are briefly described below. Prescriptive
design requirements for adobe masonry are contained
in Section 2109.8.
Adobe, stabilized. Admixtures are added to the soil
to produce more durable units.
Adobe, unstabilized. Unstabilized adobe does not
contain stabilizers in the soil and is, therefore, not as durable as stabilized adobe.
ANCHOR. Metal rod, wire or strap that secures masonry to its
structural support.
v Anchors are fasteners connecting two components.
Figure 2102.1(1) shows examples of anchor bolts that
can be used in masonry and Figure 2102.1(3) shows
some uses of anchor bolts to connect wood floors and
masonry walls.
In this chapter, anchors are required where masonry
walls meet intersecting walls, floors, roofs or the foundation below. Requirements for strength and durability
of metal anchors are given in Section 2103.11.
ARCHITECTURAL TERRA COTTA. Plain or ornamental
hard-burned modified clay units, larger in size than brick, with
glazed or unglazed ceramic finish.
v Architectural terra cotta refers to fired clay units with architectural shape and fired glazed coating. While rarely
used today in new construction, repairs to terra cotta in
existing building construction are not uncommon.
These clay masonry units are usually produced for custom-made, anchored, ornamental veneers.
AREA.
Bedded. The area of the surface of a masonry unit that is in
contact with mortar in the plane of the joint.
Gross cross-sectional. The area delineated by the out-to-out
specified dimensions of masonry in the plane under
consideration.
Net cross-sectional. The area of masonry units, grout and
mortar crossed by the plane under consideration based on
out-to-out specified dimensions.
v Area. Different areas are used in different calculations
throughout this chapter. It is important to use the correct
21-4
HEX HEAD
SQUARE HEAD
( A ) HEADED BOLTS
“L” BOLT
“J” BOLT
( B ) BENT BOLTS
SQUARE PLATE ANCHOR BOLT
CIRCULAR PLATE ANCHOR BOLT
PLATE
ANCHORS
NOT PERMITTED
FOR STRENGTH
DESIGN OF
MASONRY
ANCHOR
BOLTS
( C ) PLATED BOLTS
Figure 2102.1(1)
ANCHOR BOLTS
area, as each different area may give dramatically different results that may not be appropriate.
Bedded. The bedded area is simply the area of the
unit’s surface on which mortar is placed and through
which stresses are transferred to the adjacent work.
Gross cross-sectional. The gross cross-sectional
area of the masonry is the specified masonry width
(thickness) multiplied by the specified length, as illustrated in Figure 2102.1(2). While subtraction of core areas of the masonry unit is not required, subtraction of
the space between wythes is required in noncomposite
walls. Empirical compressive stress design is based on
the gross cross-sectional area of the masonry.
Net cross-sectional. The net cross-sectional area encompasses the area of units, grout and mortar contained within the plane under consideration. For
ungrouted masonry, this area is sometimes equal to the
bedded area, or more often to the minimum specified
area of the face shells. For grouted masonry, this also
includes that area of cores, cells or spaces filled with
grout.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
FIGURE 2102.1(2) – FIGURE 2102.1(3)
BED JOINT. The horizontal layer of mortar on which a masonry unit is laid.
BOND BEAM. A horizontal grouted element within masonry
in which reinforcement is embedded.
v This is a horizontal mortar joint [see Figure 2102.1(4)]
that separates a course of masonry units from the ones
above and supports the weight of the masonry. Unlike
the head or collar joint, it is easily closed when the masonry unit is placed. For a masonry unit in the typical
(stretcher) orientation, the bed joint faces are the top
and bottom, while the bed surface of the masonry unit is
the underside. A special type of bed joint is the
base-course joint or starting joint placed over foundations. See Section 2104.1.2 for requirements for thicknesses, placement and permitted tolerances for bed
joints.
v Bond beams permit horizontal reinforcement to be
placed in masonry. For hollow masonry unit walls, special units can either be manufactured or the webs and
end shells can be reduced by saw cutting to allow horizontal reinforcing bars to be placed in the wall.
BOND REINFORCING. The adhesion between steel reinforcement and mortar or grout.
v This term describes the adhesion between reinforcing
steel and grout or mortar that transfers stresses between those elements.
SPECIFIED LENGTH
CLAY OR SHALE MASONRY
SPECIFIED WIDTH (THICKNESS)
SPECIFIED LENGTH
CONCRETE MASONRY
SPECIFIED WIDTH (THICKNESS)
GROSS AREA = SPECIFIED LENGTH × SPECIFIED THICKNESS
Figure 2102.1(2)
MASONRY/FLOOR ANCHOR BOLT CONNECTOR
MASONRY WALL
MASONRY WALL
ANCHOR BOLT CONNECTING
FLOOR TO MASONRY WALL
ANCHOR BOLT CONNECTING
FLOOR TO MASONRY WALL
WOOD JOIST
GROUT-FILLED CORES OR
SOLID CONCRETE MASONRY
APPROVED JOIST HANGER
WOOD LEDGER
Figure 2102.1(3)
GROSS CROSS-SECTIONAL AREA FOR SINGLE WYTHE WALL UNDER LOAD
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-5
FIGURE 2102.1(4)
MASONRY
JOINT REINFORCEMENT
JOINT REINFORCEMENT
CMU WYTHE
HEAD JOINT
COLLAR JOINT
BRICK WYTHE
HEAD JOINT
BED JOINT
COLLAR JOINT
Figure 2102.1(4)
MASONRY CONSTRUCTION TERMS
BRICK.
Calcium silicate (sand lime brick). A masonry unit made of
sand and lime.
Clay or shale. A masonry unit made of clay or shale, usually
formed into a rectangular prism while in the plastic state and
burned or fired in a kiln.
members, they are used to limit the unbraced horizontal
length of walls (and their corresponding length-to-thickness ratios) by providing horizontally spaced points of lateral support. As lateral-load-resisting beam elements, or
as vertical-load-resisting beam columns built integrally
with the wall, they are primary structural members.
Concrete. A masonry unit having the approximate shape of a
rectangular prism and composed of inert aggregate particles
embedded in a hardened cementitious matrix.
CAST STONE. A building stone manufactured from portland
cement concrete precast and used as a trim, veneer or facing on
or in buildings or structures.
v Brick is composed of masonry units that are generally
prismatic (rectangular) in shape.
v Cast stone is a simulated stone precast from portland
cement concrete. This material is typically used for veneer, but can also be used in other applications.
Calcium silicate brick (sand lime brick). This solid
brick unit is made principally from high-silica sand and
lime.
Clay or shale. These masonry units are manufactured
from surface clay, shale or fire clay. Different manufacturing processes and physical properties are associated with each material. Surface clays are found in
sedimentary layers near the surface. Shales are clays
subjected to geologic pressure, resulting in a solid state
similar to slate. Fire clays are mined from deeper layers, resulting in more uniform properties. These units
are formed into the desired shape by extrusion, molding or pressing. They are then fired in a kiln to increase
their strength and durability.
Concrete. Concrete brick units are made from a zeroslump mix of portland cement and possibly other
cementitious materials, aggregates, water and admixtures. These units are solid or have a shallow depression
called a frog. Slump brick, for example, is a decorative
concrete brick with bulged sides resulting from the consistency of the mix and the manufacturing process.
BUTTRESS. A projecting part of a masonry wall built integrally therewith to provide lateral stability.
v These elements serve one or more purposes and are
sometimes called “pilasters.” As secondary structural
21-6
CELL. A void space having a gross cross-sectional area greater
than 11/2 square inches (967 mm2).
v This term defines a large intentional void within a masonry unit. Grout and reinforcing steel are often placed
in cells to form reinforced masonry.
CHIMNEY. A primarily vertical enclosure containing one or
more passageways for conveying flue gases to the outside atmosphere.
v A chimney is a primarily vertical enclosure containing
one or more flues. This chapter regulates masonry
chimneys and fireplaces in Sections 2111 through 2113.
Chimneys differ from metal vents in the materials from
which they are constructed and the type of appliance
they are designed to serve. Chimneys can vent much
hotter flue gases than metal vents.
CHIMNEY TYPES.
High-heat appliance type. An approved chimney for removing the products of combustion from fuel-burning,
high-heat appliances producing combustion gases in excess
of 2,000°F (1093°C) measured at the appliance flue outlet
(see Section 2113.11.3).
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
Low-heat appliance type. An approved chimney for removing the products of combustion from fuel-burning, low-heat
appliances producing combustion gases not in excess of
1,000°F (538°C) under normal operating conditions, but capable of producing combustion gases of 1,400°F (760°C)
during intermittent forces firing for periods up to 1 hour.
Temperatures shall be measured at the appliance flue outlet.
Masonry type. A field-constructed chimney of solid masonry units or stones.
Medium-heat appliance type. An approved chimney for removing the products of combustion from fuel-burning, medium-heat appliances producing combustion gases not exceeding 2,000°F (1093°C) measured at the appliance flue
outlet (see Section 2113.11.2).
v Provisions for several types of chimneys are contained
in Chapter 21, as described below.
High-heat appliance type. High-heat chimneys are
used in industrial applications, such as incinerators,
kilns and blast furnaces. Section 2113.11.3 contains requirements for the construction and installation of chimneys for high-heat appliances.
Low-heat appliance type. Most domestic fuel-burning
appliances are low-heat appliances. Low-heat appliances include solid-fuel-burning appliances, such as
room heaters and wood stoves. Section 2113 contains
requirements for the construction and installation of
chimneys for low-heat appliances.
Masonry type. Masonry chimneys can have one or
more flues and are field constructed of masonry units,
stone, concrete and fired-clay materials. Masonry
chimneys can stand alone or be part of a masonry fireplace. Section 2113 contains requirements for the construction and installation of masonry chimneys.
Most masonry chimneys require a chimney liner,
resistant to heat and the corrosive action of the products of combustion. Chimney liners are generally made
of fired-clay tile, refractory brick, poured-in-place refractory materials or stainless steel.
Medium-heat appliance type. Some examples of medium-heat appliances are annealing furnaces, galvanizing furnaces, pulp dryers and charcoal furnaces.
Section 2113.11.2 contains requirements for the construction and installation of chimneys for medium-heat
appliances.
CLEANOUT. An opening to the bottom of a grout space of sufficient size and spacing to allow the removal of debris.
v These openings allow debris to be removed from a
space to be grouted. The code references ACI
530.1/ASCE 6/TMS 602 for minimum construction requirements for masonry, including the minimum size
and maximum spacing of cleanouts for grouted masonry.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2102.1
COLLAR JOINT. Vertical longitudinal joint between wythes
of masonry or between masonry and backup construction that is
permitted to be filled with mortar or grout.
v A collar joint is a filled space between masonry wythes
[see Figure 2102.1(4)]. Care is necessary for proper
construction of collar joints, especially where solid filling
is required.
COLUMN, MASONRY. An isolated vertical member whose
horizontal dimension measured at right angles to its thickness
does not exceed three times its thickness and whose height is at
least four times its thickness.
v Masonry columns typically resist moment and axial
compression and sometimes axial tension from uplift.
Masonry elements falling within the dimensional limits
for columns must be designed and detailed accordingly,
with minimum column ties and minimum vertical reinforcement.
The requirements for masonry columns vary. Some
members meeting the geometric requirements for columns do not have significant structural demands placed
on them. In light of this, Section 2107.2.2 exempts some
column-type elements from these column detailing
requirements.
COMPOSITE ACTION. Transfer of stress between components of a member designed so that in resisting loads, the combined components act together as a single member.
v This definition is needed in order to fully explain what is
meant by composite masonry.
COMPOSITE MASONRY. Multiwythe masonry members
acting with composite action.
v When masonry wythes are connected or bonded together so that stresses can be transferred adequately
between them, the masonry is considered as composite
masonry. Section 2.1.3.2 of ACI 530/ASCE 5/TMS 402
provides minimum bonding requirements for masonry
to be considered as composite.
COMPRESSIVE STRENGTH OF MASONRY. Maximum
compressive force resisted per unit of net cross-sectional area of
masonry, determined by the testing of masonry prisms or a function of individual masonry units, mortar and grout.
v The specified compressive strength of masonry, f ′m, is
used for the engineered design of masonry (working
stress design of Section 2107 and strength design of
Section 2108). The average compressive strength of
masonry, determined by the prism test method or the
unit strength method (Section 2105.2), must equal or
exceed the specified compressive strength.
CONNECTOR. A mechanical device for securing two or more
pieces, parts or members together, including anchors, wall ties
and fasteners.
v A few types of steel connectors are illustrated in Figures
2102.1(2) and 2102.1(4). Masonry connectors attach
21-7
FIGURE 2102.1(5)
MASONRY
COVER. Distance between surface of reinforcing bar and edge
of member.
v An adequate thickness of masonry materials is needed
between reinforcing steel and the surface of the masonry for two important reasons. The first reason is for
proper transfer of stresses between the reinforcing steel
and the masonry. This cover, often referred to as the
“structural cover,” is noted by the term K in Equation
21-2. The second reason is so that the reinforcement is
protected from corrosion or degradation. Accordingly,
larger cover is required in the MSJC standards for masonry with more severe exposure.
DIAPHRAGM. A roof or floor system designed to transmit lateral forces to shear walls or other lateral-load-resisting elements.
v A diaphragm is a planar horizontal structural element
(for example, a floor or roof) designed to transmit horizontal forces to vertical resisting elements (for example,
shear walls or frames). Diaphragms are essential elements in the lateral-load-resisting system of a structure.
Diaphragms are considered as rigid or flexible in their
own planes. Flexible diaphragms deflect more than rigid
diaphragms under imposed loads.
DIMENSIONS.
Specified. The dimensions specified for the manufacture or
construction of masonry, masonry units, joints or any other
component of a structure.
v Different dimensions are used to designate sizes of masonry units and masonry elements. The terms below
denote the common meanings of various types of dimensions used in the chapter.
Actual. The actual dimensions of a masonry unit are its
measured dimensions. Actual dimensions should equal
the specified dimensions within the construction or manufacturing tolerances.
Nominal. The nominal dimensions of a masonry unit are
the specified dimensions, plus the specified thickness of
one mortar joint. Nominal dimensions are used for architectural layout of masonry structures. Figure 2102.1(5)
shows nominal dimensions for a specific concrete masonry unit.
Specified. The specified dimensions are prescribed in
the construction documents. Actual dimensions should
equal the specified dimensions, within the construction
or manufacturing tolerances. Figure 2102.1(5) shows
specified and nominal dimensions for a concrete masonry unit.
EFFECTIVE HEIGHT. For braced members, the effective
height is the clear height between lateral supports and is used for
calculating the slenderness ratio. The effective height for unbraced members is calculated in accordance with engineering
mechanics.
v Effective height is a theoretical distance used to predict
the buckling load (compressive capacity as governed by
7 5/8"
HEIGHT
Actual. The measured dimension of a masonry unit or
element.
Nominal. A dimension equal to a specified dimension plus
an allowance for the joints with which the units are to be laid.
Thickness is given first, followed by height and then length.
8" HEIGHT
intersecting components and also act as bonding elements. The specified size, grade, type and location of
connectors are required on construction documents, in
accordance with Section 2101.3.
"
7
(T
15
5/
8"
W
I
CK DTH
NE
SS
)
HI
TH
NG
LE
16
8"
(TH WID
ICK TH
NE
SS
)
SPECIFIED DIMENSIONS
For SI:
"
5/8
TH
NG
E
L
NOMINAL DIMENSIONS
(i.e., 3/8" MORTAR JOINT INCLUDED)
1 inch = 25.4 mm.
Figure 2102.1(5)
SPECIFIED AND NOMINAL DIMENSIONS FOR NOMINAL 8 × 8 × 16 CONCRETE MASONRY UNITS
21-8
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
stability) of a wall or column. For a braced condition (no
sidesway), effective height is conservatively required to be
assumed as the clear height between points of lateral support. For an unbraced condition (sidesway permitted), the
effective height is greater than the clear height and must
be calculated.
FIREPLACE. A hearth and fire chamber or similar prepared
place in which a fire may be made and which is built in conjunction with a chimney.
v Requirements for masonry fireplaces are contained in
Section 2111.
FIREPLACE THROAT. The opening between the top of the
firebox and the smoke chamber.
v This definition is necessary for proper understanding of
the code criteria for location and minimum cross-sectional area. This criterion is based on many years of
successful performance and is needed to provide
proper construction requirements (see Section 2111.7).
GROUTED MASONRY.
Grouted hollow-unit masonry. That form of grouted masonry construction in which certain designated cells of hollow units are continuously filled with grout.
Grouted multiwythe masonry. That form of grouted masonry construction in which the space between the wythes is
solidly or periodically filled with grout.
v Masonry with grout, either in the cells of hollow units or in
the collar joint, is considered grouted masonry. Grouted
masonry has a greater surface area to resist loads and a
better transfer of stresses to reinforcing steel.
Grouted hollow-unit masonry. Hollow masonry units
are often reinforced and grouted to provide stronger elements. Table 7 of ACI 530.1/ASCE 6/TMS 602 provides requirements on fine or coarse grout based on
the dimensions of the cell to be grouted.
Grouted multiwythe masonry. The space between
wythes of multiwythe masonry can be grouted to provide stronger elements. Table 7 of ACI 530.1/ASCE
6/TMS 602 provides requirements on fine or coarse
grout, based on the dimensions of the space to be
grouted.
HEAD JOINT. Vertical mortar joint placed between masonry
units within the wythe at the time the masonry units are laid.
v Vertically oriented joints between masonry units are
head joints [see Figure 2102.1(4)].
HEADER (Bonder). A masonry unit that connects two or more
adjacent wythes of masonry.
v Masonry bond between adjacent masonry wythes, and
masonry bond anchorage between intersecting masonry walls, are occasionally accomplished with connecting units called “headers” or “bonders.” The units
may be visible on the outside of either wythe, or may not
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2102.1
be visible on one or more wythes. If not visible, they are
referred to as “blind headers.” Headers must have a
minimum embedment in each wythe.
HEIGHT, WALLS. The vertical distance from the foundation
wall or other immediate support of such wall to the top of the
wall.
v This term means the actual height, measured from the
bottom to the top of the wall, for free-standing cantilever
walls, or as the vertical distance between points of lateral support for walls spanning between floor or roof
levels.
MASONRY. A built-up construction or combination of building units or materials of clay, shale, concrete, glass, gypsum,
stone or other approved units bonded together with or without
mortar or grout or other accepted method of joining.
Ashlar masonry. Masonry composed of various sized rectangular units having sawed, dressed or squared bed surfaces,
properly bonded and laid in mortar.
Coursed ashlar. Ashlar masonry laid in courses of stone of
equal height for each course, although different courses shall
be permitted to be of varying height.
Glass unit masonry. Nonload-bearing masonry composed
of glass units bonded by mortar.
Plain masonry. Masonry in which the tensile resistance of
the masonry is taken into consideration and the effects of
stresses in reinforcement are neglected.
Random ashlar. Ashlar masonry laid in courses of stone set
without continuous joints and laid up without drawn patterns.
When composed of material cut into modular heights, discontinuous but aligned horizontal joints are discernible.
Reinforced masonry. Masonry construction in which reinforcement acting in conjunction with the masonry is used to
resist forces.
Solid masonry. Masonry consisting of solid masonry units
laid contiguously with the joints between the units filled with
mortar.
v The materials (other than gypsum) and elements constructed as stated in this definition are considered masonry construction and are regulated by Chapter 21.
This term identifies the building elements of plain
(unreinforced) masonry, reinforced masonry, grouted
masonry, glass unit masonry and masonry veneer.
Ashlar masonry. Units for ashlar masonry construction are rectangular in shape but variable in size.
Coursed ashlar. In coursed ashlar masonry, all units in
one course are the same height, although different
courses may have different heights.
Glass unit masonry. Glass unit masonry is required to
be designed in accordance with Sections 2101.2.4 and
2110.
Plain masonry. Plain masonry has historically been referred to as “unreinforced masonry.” Since such ma21-9
2102.1
sonry may actually contain some reinforcement,
however, the term “unreinforced” has fallen out of favor.
When reinforcement is contained in plain masonry, its
contribution to the strength of the system is required to
be ignored. The bond between the masonry units and
mortar is critical in the performance of plain masonry.
Random ashlar. Random ashlar has discontinuous
bed joints because units have different height.
Reinforced masonry. Reinforced masonry contains reinforcement (currently limited to steel reinforcement) and
is designed considering the tensile strength of that reinforcement. Not all masonry containing reinforcement is
considered reinforced masonry. Some plain masonry
contains reinforcement (usually to reduce the size of any
cracks that may form), but the contribution of that reinforcement is required to be neglected.
Solid masonry. This term describes single- or
multi-wythe walls composed of solid masonry units, including the thickness of the collar joint if it is filled with
mortar or grout.
MASONRY UNIT. Brick, tile, stone, glass block or concrete
block conforming to the requirements specified in Section 2103.
Clay. A building unit larger in size than a brick, composed of
burned clay, shale, fired clay or mixtures thereof.
Concrete. A building unit or block larger in size than 12
inches by 4 inches by 4 inches (305 mm by 102 mm by 102
mm) made of cement and suitable aggregates.
Hollow. A masonry unit whose net cross-sectional area in
any plane parallel to the load-bearing surface is less than 75
percent of its gross cross-sectional area measured in the same
plane.
Solid. A masonry unit whose net cross-sectional area in every plane parallel to the load-bearing surface is 75 percent or
more of its gross cross-sectional area measured in the same
plane.
v Masonry units are natural stone units or manufactured
units of fired clay, shale, cementitious materials or
glass.
Clay. Clay masonry units are manufactured from fired
clay or shale (also see the definition of “Brick, clay or
shale”).
Concrete. Concrete masonry units are manufactured
from a zero-slump mixture of portland cement (and
possibly other cementitious materials), aggregates,
water and sometimes admixtures.
Hollow. Hollow masonry units are those having a specified net cross-sectional area less than 75 percent of
their corresponding gross cross-sectional area. Where
the specified net cross-sectional area is equal to or
greater than 75 percent of the gross cross-sectional
area, the unit is considered to be solid.
Solid. Solid masonry units have a specified net
cross-sectional area 75 percent or greater of their corresponding gross cross-sectional area. Where the
21-10
MASONRY
specified net cross-sectional area is less than 75
percent of the gross cross-sectional area, the unit is
considered to be hollow.
MEAN DAILY TEMPERATURE. The average daily temperature of temperature extremes predicted by a local weather bureau for the next 24 hours.
v This is the predicted average daily temperature to confirm when cold-weather and hot-weather construction
techniques are required to be followed.
MORTAR. A plastic mixture of approved cementitious materials, fine aggregates and water used to bond masonry or other
structural units.
v Mortar is the material that bonds units and accessories
together and compensates for dimensional variations of
the units. Both the plastic and hardened properties of
mortar are important for strong, durable, water-tight
construction. Material requirements and referenced
standards for several permitted mortar types are given
in Section 2103.7.
MORTAR, SURFACE-BONDING. A mixture to bond concrete masonry units that contains hydraulic cement, glass fiber
reinforcement with or without inorganic fillers or organic modifiers and water.
v This mortar is a packaged, dry, combined material permitted for use in the surface bonding of concrete masonry units that have not been prefaced, coated or
painted. Masonry units are stacked without mortar joints
and surface-bonding mortar is then applied to both
sides of the wall surface, creating a structural element.
PLASTIC HINGE. The zone in a structural member in which
the yield moment is anticipated to be exceeded under loading
combinations that include earthquakes.
v The portion of a member where the yield moment is expected to be exceeded under seismic loads is considered a plastic hinge zone. Location and detailing of
plastic hinge zones are a critical part of strength design
for seismic loads.
PRESTRESSED MASONRY. Masonry in which internal
stresses have been introduced to counteract potential tensile
stresses in masonry resulting from applied loads.
v This definition provides an understanding of the term
“prestressed masonry,” which is used to define particular types of shear wall systems recognized under the
code.
PRISM. An assemblage of masonry units and mortar with or
without grout used as a test specimen for determining properties
of the masonry.
v Compliance with the specified compressive strength of
masonry, f ′m, can be verified by prism tests. The prism
configuration and construction methods for such tests
are prescribed in ASTM C 1314.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
FIGURE 2102.1(6)
RUBBLE MASONRY. Masonry composed of roughly shaped
stones.
Coursed rubble. Masonry composed of roughly shaped
stones fitting approximately on level beds and well bonded.
Random rubble. Masonry composed of roughly shaped
stones laid without regularity of coursing but well bonded
and fitted together to form well-divided joints.
Rough or ordinary rubble. Masonry composed of unsquared field stones laid without regularity of coursing but
well bonded.
v Rubble consists of pieces of stone that are irregular in
shape and size. Rubble is often laid to form walls, foundations and paving.
Coursed rubble. Coursed rubble consists of roughly
shaped stones that are laid with continuous bed joints.
Random rubble. Random rubble has approximately
level beds, but discontinuous bed joints because of the
varying heights of the individual units.
Rough or ordinary rubble. This type of rubble is laid
without regular coursing.
RUNNING BOND. The placement of masonry units such that
head joints in successive courses are horizontally offset at least
one-quarter the unit length.
v Figure 2102.1(6) illustrates the required overlap for running bonds. The minimum overlap is necessary to provide strength between units when masonry spans horizontally. Reinforcement or reinforced bond beams are
required in Section 2109.6.5.2 for masonry in other than
running bond. Masonry not laid in running bond is often
referred to as “stackbonded.”
SHEAR WALL.
Detailed plain masonry shear wall. A masonry shear wall
designed to resist lateral forces neglecting stresses in reinforcement, and designed in accordance with Section
2106.1.1.
Intermediate prestressed masonry shear wall. A prestressed masonry shear wall designed to resist lateral forces
considering stresses in reinforcement, and designed in accordance with Section 2106.1.1.2.
Intermediate reinforced masonry shear wall. A masonry
shear wall designed to resist lateral forces considering
stresses in reinforcement, and designed in accordance with
Section 2106.1.1.
Ordinary plain masonry shear wall. A masonry shear wall
designed to resist lateral forces neglecting stresses in reinforcement, and designed in accordance with Section
2106.1.1.
Ordinary plain prestressed masonry shear wall. A prestressed masonry shear wall designed to resist lateral forces
considering stresses in reinforcement, and designed in accordance with Section 2106.1.1.1.
Ordinary reinforced masonry shear wall. A masonry
shear wall designed to resist lateral forces considering
stresses in reinforcement, and designed in accordance with
Section 2106.1.1.
Special prestressed masonry shear wall. A prestressed masonry shear wall designed to resist lateral forces considering
stresses in reinforcement and designed in accordance with
TYPICAL RUNNING BOND
CONCRETE MASONRY UNITS
TYPICAL RUNNING BOND BRICK UNITS
UNIT LENGTH
1/4 UNIT
OVERLAP
UNIT LENGTH
1/4 UNIT
OVERLAP
MASONRY THAT IS NOT OVERLAPPED A MINIMUM OF ONE-QUARTER OF THE UNIT LENGTH
IS CONSIDERED TO BE LAID IN STACK BOND.
Figure 2102.1(6)
RUNNING BOND MASONRY
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-11
2102.1
Section 2106.1.1.3 except that only grouted, laterally restrained tendons are used.
Special reinforced masonry shear wall. A masonry shear
wall designed to resist lateral forces considering stresses in
reinforcement, and designed in accordance with Section
2106.1.1.
v Shear walls are vertical diaphragms resisting vertical
and in-plane lateral loads. They are part of the lateral-force-resisting system and basic seismic-force-resisting system. The various types of shear wall systems
defined are necessary to correctly characterize their expected performance level in resisting earthquake forces
(also see the definition of “Basic seismic-force-resisting
system” in Chapter 16). Shear walls must be adequately
connected to floor and roof diaphragms and to the foundation, so that loads can be transferred effectively between these elements.
Detailed plain masonry shear wall. Such shear walls
are designed as plain (unreinforced) masonry, but contain a minimum amount of reinforcement in the horizontal and vertical directions. Because of this
reinforcement, these walls have more favorable seismic design parameters, including higher response
modification factors, R, than ordinary plain masonry
shear walls.
Intermediate prestressed masonry shear wall. This
definition distinguishes intermediate prestressed masonry shear walls from the other types of prestressed
masonry shear walls that are recognized by the code in
order to classify the lateral-force-resisting system in determining earthquake loads.
Intermediate reinforced masonry shear wall. These
shear walls are designed as reinforced masonry and
also must contain a minimum amount of prescriptive reinforcement. Because they contain reinforcement, their
seismic performance will be better than that of plain
masonry shear walls in seismic events and they are accordingly permitted in areas of moderate as well as low
seismic risk. These walls have more favorable seismic
design parameters, including higher response modification factors, R, than plain masonry shear walls and
ordinary reinforced masonry shear walls.
Ordinary plain masonry shear wall. Such shear walls
meet only minimum requirements, without minimum
amounts of horizontal and vertical reinforcement. Thus,
they may be used only in areas of low seismic risk.
Plain masonry walls are designed as unreinforced masonry (by the noted sections), although they may in fact
contain reinforcement.
Ordinary plain prestressed shear wall. This definition distinguishes ordinary plain prestressed masonry
shear walls from the other types of prestressed masonry shear walls that are recognized by the code in order to classify the lateral-force-resisting system in
determining earthquake loads.
21-12
MASONRY
Ordinary reinforced masonry shear wall. These
shear walls are designed as reinforced masonry. Because they contain reinforcement, their seismic performance is expected to be better than that of plain masonry
shear walls and they are accordingly permitted in areas of
moderate as well as low seismic risk. These walls have
more favorable seismic design parameters, including
higher response modification factors, R, than plain masonry shear walls. When used in areas of moderate
seismic risk (Seismic Design Category C), however,
minimum reinforcement is required as noted in Section
2106.4.
Special prestressed masonry shear wall. This definition distinguishes special prestressed masonry shear
walls from the other types of prestressed masonry
shear walls that are recognized by the code in order to
classify the lateral-force-resisting system in determining earthquake loads.
Special reinforced masonry shear wall. These shear
walls are designed as reinforced masonry and must
also meet prescriptive reinforcement limits and material
limitations. Because of these requirements, they are
permitted to be used in all seismic risk areas. These
walls have the most favorable seismic design parameters, including the highest response modification factors, R, of any of the masonry shear wall types.
SHELL. The outer portion of a hollow masonry unit as placed
in masonry.
v The shells of a masonry unit are defined by how the unit
is used in construction. They are the portions of a hollow
masonry unit exposed on the faces of elements and
may include face shells and end webs.
SPECIFIED. Required by construction documents.
v The construction documents contain material and construction requirements essential to the proper performance of the structure. These requirements are considered minimums and material or construction that does
not comply is not permitted by the code.
SPECIFIED
COMPRESSIVE
STRENGTH
OF
MASONRY, f ′m. Minimum compressive strength, expressed as
force per unit of net cross-sectional area, required of the masonry used in construction by the construction documents, and
upon which the project design is based. Whenever the quantity
f ′m is under the radical sign, the square root of numerical value
only is intended and the result has units of pounds per square
inch (psi) (Mpa).
v Engineered design of structural masonry is based on
the specified compressive strength of the masonry, f ′m.
This strength is required to be shown on the contract
documents. Strength of the constructed masonry, determined by the unit strength method or prism strength
method, is required to equal or exceed the specified
compressive strength of masonry.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
STACK BOND. The placement of masonry units in a bond pattern is such that head joints in successive courses are vertically
aligned. For the purpose of this code, requirements for stack
bond shall apply to masonry laid in other than running bond.
v Figure 2102.1(6) illustrates the required overlap for running bonds. If this required overlap is not provided, the
wall is considered to be laid in stack bond. Reinforcement, or reinforced bond beams, are required by Section 2109.6.5.2 for stack bond masonry.
STONE MASONRY. Masonry composed of field, quarried or
cast stone units bonded by mortar.
Ashlar stone masonry. Stone masonry composed of rectangular units having sawed, dressed or squared bed surfaces
and bonded by mortar.
Rubble stone masonry. Stone masonry composed of irregular-shaped units bonded by mortar.
v Stone masonry is comprised of natural marble, limestone, granite, sandstone and slate for building purposes. Ashlar stone is further distinguished as coursed
or random. Rubble stone masonry is further distinguished as coursed, random or rough.
Ashlar stone masonry. Units for ashlar masonry construction are rectangular in shape but variable in size.
Rubble stone masonry. Unlike ashlar stone masonry,
which has rectangular units, rubble stone masonry
units are irregular in shape. Rubble stone masonry is
further distinguished as coursed, random or rough.
STRENGTH.
Design strength. Nominal strength multiplied by a strength
reduction factor.
Nominal strength. Strength of a member or cross section
calculated in accordance with these provisions before application of any strength-reduction factors.
Required strength. Strength of a member or cross section
required to resist factored loads.
v The term “strength” is used in both general and specific
senses. In the general sense, the strength of a member
is its capacity to resist internal forces and moments. In
the specific sense, strength is further categorized by
type. The tensile strength of a member, for instance, refers to how much tensile force the member can support.
In the context of strength design, the force resulting
from factored design actions is referred to as the required strength. An approximation to the “minimum expected” strength of the member is referred to as the
“nominal strength” (see the commentary on nominal
strength). This nominal strength is then multiplied by a
strength reduction factor to account for material, design
and construction variabilities to determine the design
strength. The design strength must equal or exceed the
required strength.
In the context of working stress design, the force resulting from unfactored design loads is referred to as
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2102.1
the “applied (actual) force.” The anticipated strength
would then be reduced by appropriate safety factors to
either an allowable working stress or an allowable working strength (for example, for anchor bolts). This working stress or strength is required to equal or exceed the
applied (actual) stress or force.
“Design strength,” “Nominal strength” and “Required
strength” are defined in more detail immediately below.
Working stresses and strengths are defined in ACI
530/ACI 5/TMS 402.
Strength can also refer to the load at which a test
specimen fails (for example, prism strength).
Design strength. The strength design procedures of
Section 2108 use the term “design strength” to indicate a
realistic capacity of a member considering material, design and construction variabilities. The design strength is
obtained by multiplying the nominal strength by a strength
reduction factor. The design strength must equal or exceed the required strength (see separate definition in
Section 2102.1).
Nominal strength. The strength design procedures of
Section 2108 use the term “nominal strength” to refer to
the capacity of a masonry member, determined based
on the assumptions contained in Section 2108. It is
sometimes referred to as the “expected” strength of the
member; however, this is a misnomer. The nominal
strength would equal the expected strength if: the masonry member were constructed of materials complying exactly with the minimum material requirements,
design equations were perfect and construction tolerances were zero. Since material strengths commonly
exceed minimum requirements, expected strength is
often much higher than nominal strength. For instance,
Grade 60 reinforcement often has a yield strength of
around 66,000 psi (455 MPa), even though the minimum specified yield strength requirement is 60,000 psi
(414 MPa). Therefore, the nominal strength is not the
expected strength of the member, although it can be
grossly classified as the minimum expected strength.
Expected strength design is not included in Chapter 21
and is currently beyond the scope of the code. To determine the design strength, the nominal strength is multiplied by a strength reduction factor to account for
material, design and construction variability. The design strength is required to equal or exceed the required strength.
Required strength. In the strength design of masonry
(see Section 2108), the required strength is that which
corresponds to the factored design loads on the structure.
The design strength (nominal strength times the appropriate strength reduction factor) must equal or exceed the
required strength.
TIE, LATERAL. Loop of reinforcing bar or wire enclosing
longitudinal reinforcement.
v Lateral ties enclose longitudinal reinforcement. They are
typically used in columns to support the compression reinforcement and masonry core so that these can support
21-13
2102.1
extreme loads even with some degradation of the masonry. Reinforcement can be assumed to be effective in
carrying compressive forces only when supported by lateral ties.
Lateral ties also resist shear loads. Ties must form a
closed rectangle or loop to completely surround the longitudinal reinforcement. Stirrups, in contrast, can be open.
TIE, WALL. A connector that connects wythes of masonry
walls together.
v Ties are used to connect adjacent wythes and are subject
to requirements for strength, durability and installation.
Ties are adjustable or nonadjustable. A typical nonadjustable “Z” wire tie is shown in Figure 2109.6.3(1).
TILE. A ceramic surface unit, usually relatively thin in relation
to facial area, made from clay or a mixture of clay or other ceramic materials, called the body of the tile, having either a
“glazed” or “unglazed” face and fired above red heat in the
course of manufacture to a temperature sufficiently high enough
to produce specific physical properties and characteristics.
v Ceramic tile units are manufactured from nonmetallic
materials and fired at high temperatures to obtain specific properties. Tile is considered a thin, nonstructural
finish that must be supported by a strong, stiff,
dimensionally stable backing.
TILE, STRUCTURAL CLAY. A hollow masonry unit composed of burned clay, shale, fire clay or mixture thereof, and
having parallel cells.
v These clay masonry units are produced as end tiles and
side tiles and differ from clay brick by having required
cells with thinner webs between them.
WALL. A vertical element with a horizontal length-to-thickness ratio greater than three, used to enclose space.
Cavity wall. A wall built of masonry units or of concrete, or a
combination of these materials, arranged to provide an airspace within the wall, and in which the inner and outer parts
of the wall are tied together with metal ties.
Composite wall. A wall built of a combination of two or
more masonry units bonded together, one forming the
backup and the other forming the facing elements.
Dry-stacked, surface-bonded walls. A wall built of concrete masonry units where the units are stacked dry, without
mortar on the bed or head joints, and where both sides of the
wall are coated with a surface-bonding mortar.
Masonry-bonded hollow wall. A wall built of masonry
units so arranged as to provide an airspace within the wall,
and in which the facing and backing of the wall are bonded
together with masonry units.
Parapet wall. The part of any wall entirely above the roof
line.
v Masonry walls typically enclose space. They are generally required to be designed and installed for weather
resistance, durability and adequate structural strength.
21-14
MASONRY
The given dimensional requirements differentiate walls
from columns.
Cavity wall. Cavity walls are made up of solid or hollow
masonry units separated by a continuous airspace or
cavity. This continuous airspace adds insulating value
and acts as a barrier to moisture when detailed with
flashing and weep holes. In many cavity walls, thermal
insulation is placed between the wythes to further enhance thermal efficiency.
Composite wall. A composite wall is a multiwythe wall
with wythes that act together to resist loads. The distinction of having wythes with different mechanical
properties is important in engineering design. Walls
constructed of different materials must be evaluated for
lateral- and vertical-load-bearing performance and for
differential movement between the wythes.
Dry-stacked, surface-bonded walls. Although this
type of wall is dry stacked, a leveling course must be set
in a full bed of mortar. Dry-stacked walls are also required to be placed in a running bond pattern (see commentary to the definition of “Mortar, surface-bonding”).
Masonry-bonded hollow wall. Hollow walls are similar to cavity walls in that they are made up of solid or
hollow units separated by an airspace. Unlike a cavity
wall, however, the wythes are bonded together by masonry units, which causes the wythes to act together
under load.
Parapet wall. These portions of masonry walls project
above the roof. A parapet wall is exposed to weather on
both sides and is laterally unsupported at the top. Parapets often have copings.
WEB. An interior solid portion of a hollow masonry unit as
placed in masonry.
v The webs of hollow units are provided to support and
strengthen the face shells. Web heights are permitted to
be reduced so that horizontal reinforcement can be
placed in the element.
WYTHE. Each continuous, vertical section of a wall, one masonry unit in thickness.
v Sometimes referred to as a “leaf” or “tier,” each wythe is
one thickness of a masonry unit.
NOTATIONS.
An = Net cross-sectional area of masonry, square inches
(mm2).
b
= Effective width of rectangular member or width of
flange for T and I sections, inches (mm).
db = Diameter of reinforcement, inches (mm).
fr = Modulus of rupture, psi (MPa).
fy = Specified yield stress of the reinforcement or the anchor
bolt, psi (MPa).
f′m = Specified compressive strength of masonry at age of 28
days, psi (MPa).
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
K
Ls
Lw
ld
lde
Pw
t
Vn
Vu
W
γ
rn
ρmax
φ
= The lesser of the masonry cover, clear spacing between
adjacent reinforcement, or five times db, inches (mm).
= Distance between supports, inches (mm).
= Length of wall, inches (mm).
= Required development length of reinforcement, inches
(mm).
= Embedment length of reinforcement, inches (mm).
= Weight of wall tributary to section under consideration,
pounds (N).
= Specified wall thickness dimension or the least lateral
dimension of a column, inches (mm).
= Nominal shear strength, pounds (N).
= Required shear strength due to factored loads, pounds
(N).
= Wind load, or related internal moments in forces.
= Reinforcement size factor.
= Ratio of distributed shear reinforcement on plane perpendicular to plane of Amv.
= Maximum reinforcement ratio.
= Strength reduction factor.
v Explanations of notations used in Chapter 21 listed
above clarify the differences among these terms and
the appropriate units, if any, that apply to them.
SECTION 2103
MASONRY CONSTRUCTION MATERIALS
2103.1 Concrete masonry units. Concrete masonry units shall
conform to the following standards: ASTM C 55 for concrete
brick; ASTM C 73 for calcium silicate face brick; ASTM C 90
for load-bearing concrete masonry units or ASTM C 744 for
prefaced concrete and calcium silicate masonry units.
v Proper selection of materials is essential to produce masonry with adequate strength and durability. This section
sets forth prescriptive and performance-based requirements (referenced standards) for masonry materials. Test
procedures and criteria for establishing and verifying quality are included. Concrete masonry refers to solid and hollow concrete units, including concrete brick, concrete
block, split-face block, slump block and other special units.
This section requires conformance to ASTM standards for
each specific type of concrete masonry unit. The standards include requirements for materials; manufacture;
physical properties; moisture content; strength; absorption; minimum dimensions and permissible variations; inspection; testing and rejection.
Concrete masonry units are selected based on the
desired use and appearance. Units are typically specified by weight, type and strength.
Hollow load-bearing concrete masonry units are
manufactured in accordance with the requirements of
ASTM C 90 using portland cement, water and mineral
aggregates. Other suitable materials, such as approved
admixtures, are permitted in accordance with ASTM C
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2103 – 2103.1
90.
Hollow load-bearing concrete masonry units have
three weight classifications: normal-weight units of 125
pounds per cubic foot (pcf) (2000 kg/m3) or more; medium-weight units of between 105 pcf (1680 kg/m3) and
125 pcf (2000 kg/m3) and lightweight units of less than
105 pcf (1680 kg/m3). Lightweight aggregates generally
are expanded blast-furnace slag or similar suitable materials. Normal-weight units are made from sand,
gravel, crushed stone or air-cooled, blast-furnace-slag
aggregates.
Hollow load-bearing concrete masonry units are classified into two types. Type I are moisture-controlled
units complying with the moisture-content requirements
of ASTM C 90; Type II are nonmoisture-controlled units.
Concrete brick is required to comply with ASTM C 55.
Concrete building brick and other solid concrete veneer
and facing units are typically smaller than concrete masonry units conforming to ASTM C 90. They are made
from portland cement, water and mineral aggregates,
with or without inclusion of other approved materials.
Concrete brick is manufactured as lightweight, medium-weight and normal-weight units as described
above for hollow concrete masonry units. Concrete
brick is manufactured in two grades: Grade N and
Grade S. Grade N units are used as architectural veneer and facing units in exterior walls, where high
strength and resistance to moisture penetration and
freeze-thaw cycling are required. Grade S units are
used when moderate strength and resistance to
freeze-thaw action and moisture penetration are required.
These units are classified into two types for each of
the grades defined. Type I are moisture-controlled units
complying with the moisture-content requirements of
ASTM C 55. Type II are nonmoisture-controlled units.
Calcium silicate face brick is a solid masonry unit
complying with ASTM C 73. These units are manufactured principally from silica sand, hydrated lime and water.
Calcium silicate face brick is manufactured in two
grades: Grade SW and Grade MW. Grade SW is required where exposure to moisture in the presence of
freezing temperatures is anticipated. Grade MW is permitted where the anticipated exposure has freezing
temperatures, but without water saturation.
Grade SW units have a minimum permitted compressive strength on the gross area of 4,500 pounds per
square inch (psi) (31.0 MPa) (average of three units),
but not less than 3,500 psi (24.1MPa) for any individual
unit. Grade MW units have a minimum permitted compressive strength on the gross area of 2,500 psi (17.2
MPa) (average of three units), but not less than 2,000
psi (13.8 MPa) for any individual unit.
ASTM C 744 is referenced for the manufacture of
prefaced concrete and calcium silicate masonry units,
commonly referred to as “glazed” concrete masonry
units. The specified exposed surfaces of these units are
covered during their manufacture with resin, resin and
inert filler or cement and inert filler to produce a smooth
21-15
2103.2
resinous tile-like facing.
Facing requirements of that standard address resistance to chemicals; failure of adhesion of the facing material; abrasion surface-burning characteristics, color and
color change; soiling and cleansability. The standard also
covers dimensional tolerances, including face dimensions
and distortions.
2103.2 Clay or shale masonry units. Clay or shale masonry
units shall conform to the following standards: ASTM C 34 for
structural clay load-bearing wall tile; ASTM C 56 for structural
clay nonload-bearing wall tile; ASTM C 62 for building brick
(solid masonry units made from clay or shale); ASTM C 1088
for solid units of thin veneer brick; ASTM C 126 for ceramic-glazed structural clay facing tile, facing brick and solid
masonry units; ASTM C 212 for structural clay facing tile;
ASTM C 216 for facing brick (solid masonry units made from
clay or shale) and ASTM C 652 for hollow brick (hollow masonry units made from clay or shale).
Exception: Structural clay tile for nonstructural use in fireproofing of structural members and in wall furring shall not
be required to meet the compressive strength specifications.
The fire-resistance rating shall be determined in accordance
with ASTM E 119 and shall comply with the requirements of
Table 602.
v Section 2103.2 requires conformance with ASTM standards for masonry units manufactured from clay or shale.
The various standards also include requirements for materials; manufacture; physical properties; minimum dimensions and permissible variations; inspections and testing.
Clay or shale masonry units are manufactured from
clay and shale, which are compounds of silica or alumina. Shale is simply a hardened clay. The raw materials are formed into the desired shape by extrusion and
cutting, molding or pressing while in the plastic state.
The units are then fired in a kiln. The raw materials and
the manufacturing process influence the physical properties of the manufactured unit.
Clay or shale masonry units are selected for their intended use from a variety of shapes, sizes and
strengths. Units are specified based on grades and
type.
Solid face brick units are required to conform to
ASTM C 216. This standard covers clay brick intended
to be used in masonry and supplying structural or facing
components, or both, to the structure. These units are
available in a variety of sizes, textures, colors and
shapes.
ASTM C 216 contains requirements for two grades of
durability: Grade SW and Grade MW. Grade SW brick is
intended for use where high and uniform resistance to
damage caused by freeze-thaw cycling is desired and
where the brick may be subjected to such cycling while
saturated with water. Grade MW brick is intended for
use where moderate resistance to cyclic freeze-thaw
damage is permissible or where the brick may be damp
but not saturated with water when such cycling occurs.
ASTM C 216 further classifies face brick into three types
of appearance: Types FBS, FBX and FBA. Type FBS
21-16
MASONRY
(face brick standard) units are permitted for general use
in masonry. Type FBX (face brick select) units are also
for general use, but have a higher degree of precision
and lower permissible variation in size than Type FBS
units. Type FBA (face brick architectural) units are also
for general use, but are intentionally manufactured to
produce characteristic architectural effects resulting
from nonuniformity in size and texture of the units.
Solid units of building brick are required to conform to
ASTM C 62. This specification covers brick intended for
use in both structural and nonstructural masonry where
external appearance is not critical. This brick was formerly called “common brick,” and the standard does not
contain appearance requirements.
ASTM C 62 contains requirements for three grades of
durability: Grade SW, Grade MW and Grade NW. Grade
SW brick is intended for use where high and uniform resistance to freeze-thaw damage is desired and where
the brick may be subjected to such cycling while saturated with water. Grade MW brick is intended for use
where moderate resistance to cyclic freeze-thaw damage is permissible or where the brick may be damp but
not saturated with water when such cycling occurs.
Grade NW is used where little resistance to cyclic
freeze-thaw damage is required and is acceptable for
applications protected from water absorption and freezing.
Hollow brick is required to conform to ASTM C 652,
which regulates hollow building and hollow facing brick.
Hollow brick differs from structural clay tile in that it has
more stringent physical property requirements, such as
thicker shell and web dimensions and higher minimum
compressive strengths.
Hollow brick has two grades of durability: Grade SW
and Grade MW. Grade SW is used where a high and
uniform degree of resistance to freeze-thaw degradation and disintegration by weathering is desired and
when the brick may be saturated while frozen. Grade
MW is intended for use where a moderate and somewhat nonuniform degree of resistance to freeze-thaw
degradation is permissible.
ASTM C 652 also classifies hollow brick into four
types of appearance: HBS, HBX, HBA and HBB. Type
HBS (hollow brick standard) units are permitted for general use. Type HBX (hollow brick select) units are also
for general use, but have a higher degree of dimensional precision than Type HBS units. Type HBA (hollow
brick architectural) units are also for general use, but
are intentionally manufactured to produce characteristic
architectural effects resulting from nonuniformity in size
and texture of the units. Type HBB (hollow building
brick) units are for general use in masonry where a particular color, texture, finish, uniformity or limits on
cracks, warpage or other imperfections detracting from
their appearance are not a consideration.
ASTM C 1088 regulates thin brick used in adhered
veneer having a maximum actual thickness of 13/4
inches (44 mm). Thin veneer brick units are specified in
three types of appearance and two grades of durability.
Exterior-grade units are for exposure to weather;
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
interior-grade units are not. Type TBS (standard) units
are permitted for general use. Type TBX (select) units
are also for general use, but have a higher degree of
precision and lower permissible variation in size than
Type TBS units. Type TBA (architectural) units are also
for general use, but are intentionally manufactured to
produce characteristic effects in variations of size, color
and texture.
ASTM C 34 is referenced for the manufacture of structural clay load-bearing wall tile. This type of tile has two
grades. Grade LBX is suitable for general use in masonry
construction and can be used in masonry exposed to
weathering, provided that the units meet durability requirements for Grade SW of ASTM C 216 for solid units of face
brick. This tile grade is also suitable for the direct application of stucco.
Grade LB is suitable for general use in masonry not exposed to freeze-thaw action, or for exposed masonry
where protected with a minimum 3-inch (76 mm) facing of
stone, brick or other masonry materials.
Fire-resistant tile intended for use in load-bearing masonry is required to conform to ASTM C 34. Tile intended
for use in fireproofing structural members is required to be
of such sizes and shapes as to cover completely the exposed surfaces of the members.
ASTM C 212, the referenced standard regulating structural clay facing tile, covers two types of structural clay
load-bearing facing tile: Types FTX and FTS.
Type FTX clay facing tile is a smooth-face tile suitable
for use in exposed exterior and interior masonry walls and
partitions where low absorption, easy cleaning and resistance to staining are required. The physical characteristics
of this tile require a high degree of mechanical perfection,
narrow color range and minimum variation in face dimensions.
Type FTS clay facing tile is a smooth- or rough-textured
face tile suitable for general use in exposed exterior and
interior masonry walls and partitions where moderate absorption, variation in face dimensions, minor defects in
surface finish and moderate color variations are permissible.
There are two classes of tile for the types stated above:
standard (for general use) and special duty (having superior resistance to impact and moisture transmission and
supporting greater lateral and vertical loads).
ASTM C 56 is the standard regulating the manufacture
of nonload-bearing tile, which is made from the same materials as other types of tile previously mentioned and is
used for partitions, fireproofing and furring.
ASTM C 126 prescribes requirements for ceramic-glazed structural clay load-bearing facing tile and
brick and other solid masonry units made from clay, shale,
fire clay or combinations thereof. The standard specifies
two grades and two types of ceramic-glazed masonry:
Grade S is used with comparatively narrow mortar joints,
while Grade SS is used where variations in face dimensions are very small; Type I units are used where only one
finished face is to be exposed, while Type II units are used
where both finished faces are to be exposed.
The finish of glazed units is important. Requirements
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2103.3 – 2103.4
and test methods are prescribed for imperviousness,
opacity, resistance to fading and crazing, hardness, abrasion resistance and flame spread smoke density. Compressive strength requirements, dimensional tolerances
and permissible distortions are also prescribed by the
standard.
The exception to this section allows structural clay tile
that does not meet the compressive strength specifications to be used as nonstructural fireproofing for structural
members. The fire-resistance rating must be determined
in accordance with ASTM E 119.
2103.3 Stone masonry units. Stone masonry units shall conform to the following standards: ASTM C 503 for marble building stone (exterior): ASTM C 568 for limestone building stone;
ASTM C 615 for granite building stone; ASTM C 616 for sandstone building stone or ASTM C 629 for slate building stone.
v Many types of natural stone, including marble, granite,
slate, limestone and sandstone, are used in building
construction. This section covers natural stones that are
sawed, cut, split or otherwise shaped for masonry purposes. Natural stones for building purposes are specified in various grades, textures and finishes and are required to have physical properties appropriate to their
intended use.
Where applicable to specific kinds of natural stone,
the finished units are required to be sound and free from
spalls, cracks, open seams, pits and other defects that
would impair structural strength and durability and,
when applicable, fire resistance.
This section requires conformance to the following
ASTM standards for natural stone masonry: ASTM C
503 for marble building stone (exterior); ASTM C 568 for
limestone building stone; ASTM C 615 for granite building stone; ASTM C 616 for sandstone building stone or
ASTM C 629 for slate building stone. The standards
contain requirements for absorption, density (except for
slate), compressive strength (except for slate), modulus
of rupture, abrasion resistance (except for granite) and
acid resistance (slate only).
2103.4 Ceramic tile. Ceramic tile shall be as defined in, and
shall conform to the requirements of, ANSI A137.1.
v Ceramic tile is made from clay, possibly mixed with
other ceramic materials. Metallic oxides may be included for glaze coloring. Ceramic tile products are
available in a broad range of sizes, appearances, characteristics and function.
ANSI A137.1 is the recognized industry standard for
the manufacture, testing and labeling of ceramic tile.
According to this standard, tile should be shipped in
sealed cartons with the grade of contents indicated by
grade seals with a distinctive coloring: blue for standard
grade (units as perfect and free from defects as is possible in the manufacturing process) and yellow for “seconds” (units having slight defects, but free from structural defects and cracks).
ANSI A137.1 groups ceramic tile into four major
21-17
2103.5 – 2103.7
types: glazed wall tile, mosaic tile, quarry tile and paving
tile.
2103.5 Glass unit masonry. Hollow glass units shall be partially evacuated and have a minimum average glass face thickness of 3/16 inch (4.8 mm). Solid glass-block units shall be
provided when required. The surfaces of units intended to be in
contact with mortar shall be treated with a polyvinyl butyral
coating or latex-based paint. Reclaimed units shall not be used.
v Consensus national standards have not been written to
establish minimum material properties or test methods
for glass blocks. Reliance must be placed on the manufacturer’s specifications and glass block is required to
meet the minimum specified dimensions of those specifications. Glass block has generally performed well in
service.
2103.6 Second-hand units. Second-hand masonry units shall
not be reused unless they conform to the requirements of new
units. The units shall be of whole, sound materials and free from
cracks and other defects that will interfere with proper laying or
use. Old mortar shall be cleaned from the unit before reuse.
v This section allows for the use of salvaged brick and
other second-hand masonry units, provided that their
quality and condition meet the requirements for new
masonry units. Second-hand units must be whole, of
sound material, clean and free from defects that would
interfere with proper laying or use.
Most second-hand masonry units come from the demolition of old buildings. Masonry units manufactured in
the past do not generally compare with the quality of
masonry made by modern manufacturing methods under controlled conditions. Therefore, designers should
expect salvaged masonry units to have lower strength
and durability than new units.
Generally, the difference between walls laid up with
new masonry units and second-hand units of the same
type is the adhesion of the mortar to the masonry surfaces. When new masonry units are laid in fresh mortar,
water and fine cementitious particles are absorbed into
the masonry, thereby improving bond strength. In contrast, pores in the bed faces of second-hand masonry
units, regardless of cleaning, are filled with particles of
cement, lime and deleterious substances that impede
adequate absorption, thereby adversely affecting bond
between the mortar and the masonry.
2103.7 Mortar. Mortar for use in masonry construction shall
conform to ASTM C 270 and shall conform to the proportion
specifications of Table 2103.7(1) or the property specifications
of Table 2103.7(2). Type S or N mortar shall be used for glass
unit masonry. The amount of water used in mortar for glass unit
masonry shall be adjusted to account for the lack of absorption.
Retempering of mortar for glass unit masonry shall not be permitted after initial set. Unused mortar shall be discarded within
21/2 hours after initial mixing except that unused mortar for glass
unit masonry shall be discarded within 11/2 hours after initial
mixing.
21-18
MASONRY
v Masonry mortar bonds masonry units to form an integral
structure. Mortar provides a tight and weather-resistant
seal between units; bonds with steel joint reinforcement, ties and other metal accessories and compensates for dimensional variations in masonry units. It can
also serve aesthetic purposes through contrasts of
color, texture and shadow lines created by different
types of tooled joints.
This section of the code establishes ASTM C 270 as
the standard regulating mortar to be used in masonry
construction. The standard covers mortars for use in the
construction of nonreinforced and reinforced unit masonry structures. It specifies types of mortar and two alternative specifications—the proportion specification
and the property specification.
Type M mortar has the highest compressive and tensile bond strength. It is suitable for general use, particularly where maximum masonry compressive strength is
required and in construction that is in contact with earth.
Type S mortar is a general-purpose mortar with high
compressive and tensile bond strengths. It is often used
in reinforced masonry and in unreinforced masonry that
requires high strength to resist out-of-plane lateral
loads.
Type N mortar is a general-purpose mortar with medium compressive and tensile bond strengths. It is used
where high vertical and lateral loads are not expected.
Type O is a low-strength mortar suitable for use in
nonload-bearing construction and where the masonry
will not be subject to severe weathering or freeze-thaw
cycling.
The materials used in mortar are required to conform
to the following standard specifications referenced in
ASTM C 270, ASTM C 5, ASTM C 91, ASTM C 144,
ASTM C 150, ASTM C 207, ASTM C 595 and ASTM C
1329.
In addition to type, mortar for masonry is further classified according to its primary cementitious materials. In
portland cement-lime mortar, the cementitious materials are portland cement and hydrated mason’s lime. In
masonry-cement mortar and mortar-cement mortar, the
principal cementitious material is portland cement,
which is contained in the masonry cement and the mortar cement.
Regardless of a masonry mortar’s principal
cementitious constituents, each ingredient—cement,
lime (when used), sand and water—contributes to the
mortar’s overall performance. Portland cement, mortar
cement, masonry cement or blended hydraulic cement
make the hardened mortar strong and durable. Lime
contributes to the workability and water retention of
fresh mortar and to the flexibility, compressive strength
and tensile bond strength of hardened mortar. Sand
serves as a filler material, increases strength and reduces shrinkage. Water determines the consistency of
fresh mortar and also hydrates the cementitious materials, resulting in hardening of the mortar.
Tables 2103.7(1) and 2103.7(2) are based on Tables
1 and 2 of ASTM C 270. These tables provide requirements for the production of mortar by the proportion
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
method (by volume) and by the property method (by
compressive strength and other properties), respectively. Whether the proportion or property specification
governs depends on the contract documents. When
neither proportion nor property specification is prescribed, the proportion specification governs, unless
data are presented to and accepted by the specifier to
show that mortar meets the requirements of the property specification.
ASTM C 270 also covers materials and testing requirements for water retention, compressive strength
and air content.
The types of mortar recommended for use in various
types of masonry construction are shown in the appendix to ASTM C 270. The performance of masonry is influenced by mortar workability, water retentivity, bond
strength, compressive strength and long-term
deformability (creep). Each mortar type has corresponding use limitations. For example, allowable compressive stresses permitted in Section 2109.3.2 for empirical design are greater for Types M and S mortar than
for Type N mortar.
Glass-block units are required to be laid in Type S or
N mortar. Admixtures containing set accelerators or antifreeze compounds are not permitted in mortars for
glass-block masonry.
TABLE 2103.7(1). See page 21-20.
v This table prescribes proportions for each mortar type
when mortar is specified by proportion. The table covers
portland cement-lime mortars, masonry-cement mortars
and mortar-cement mortars. Materials are measured by
volume. The required volume of mason’s sand used is
based on the combined volume of all cementitious materials (including lime, if applicable).
2103.8 – TABLE 2103.9
units, surface-bonding mortar can provide resistance to
penetration by wind-driven rain.
2103.9 Mortars for ceramic wall and floor tile. Portland cement mortars for installing ceramic wall and floor tile shall comply with ANSI A108.1A and ANSI A108.1B and be of the
compositions indicated in Table 2103.9.
v This section pertains to cement mortars and organic adhesives used for setting ceramic wall and floor tiles.
Each mortar type has certain qualities that make it suitable for installing tile over different kinds of backing materials or under a certain set of conditions.
Cement mortars are “thick-bed” mortars applied in
thicknesses of 3/4 to 11/4 inches (19.1 to 32 mm) on floors
and 3/4 to 1 inch (19.1 to 25 mm) on walls to achieve the
specified slopes and flatness in the finished tile work.
Portland cement mortars are suitable for setting ceramic tile in most installations. They can be applied over
properly prepared backings of clay or concrete masonry; concrete; wood frame; rough wood floors and
plywood floors; foam insulation board; gypsum wallboard and portland cement or gypsum plaster. Cement
mortars can be reinforced with metal lath or wire mesh;
in such cases, however, additional mortar thickness
may be required. Cement mortars have good structural
strength and are not affected by prolonged contact with
water.
Complete material and installation specifications are
contained in ANSI A108.1A and A108.1B, which include
required specifications for: installation of wire lath and
scratch coats; mortar mixes, bond coat mixes and mortar application; installation methods on floors, walls and
countertops; grouting of tile and general requirements
for tile installations.
TABLE 2103.9
CERAMIC TILE MORTAR COMPOSITIONS
TABLE 2103.7(2). See page 21-20.
v This table prescribes minimum required physical properties of plastic and hardened mortar for each type
when mortar is specified by property. The table covers
portland cement-lime mortars, masonry-cement mortars and mortar-cement mortars. The specified properties are compressive strength, water retention and air
content. Values are for mortars prepared in a laboratory
in accordance with ASTM C 270. These values do not
directly relate to specimens of field mortar tested in accordance with ASTM C 780.
2103.8 Surface-bonding mortar. Surface-bonding mortar shall
comply with ASTM C 887. Surface bonding of concrete masonry units shall comply with ASTM C 946.
v Specifications for materials to be used in premixed surface-bonding mortar and for the properties of the mortar
are contained in ASTM C 887. Requirements for masonry units and other materials used in constructing
dry-stacked, surface-bonded masonry for walls and for
the construction itself are contained in ASTM C 946.
In addition to its primary function of bonding masonry
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
LOCATION
MORTAR
COMPOSITION
Scratchcoat
1 cement; 1/5 hydrated lime;
4 dry or 5 damp sand
Setting bed and
leveling coat
1 cement; 1/2 hydrated lime;
5 damp sand to 1 cement
1 hydrated lime, 7 damp sand
Floors
Setting bed
1 cement; 1/10 hydrated lime;
5 dry or 6 damp sand; or 1
cement; 5 dry or 6 damp sand
Ceilings
Scratchcoat and
sand bed
1 cement; 1/2 hydrated lime;
21/2 dry sand or 3 damp sand
Walls
v Portland cement-lime mortars are a mixture of portland
cement (ASTM C 150), hydrated lime (ASTM C 207)
and damp mason’s sand (ASTM C 144). Proportions of
these ingredients are given in Table 2103.9, dealing
with the portland cement-lime mortars most commonly
used for setting ceramic tile on wall, floor and ceiling
construction and measured in parts by volume. Complete material and installation specifications are contained in ANSI A108.1.
21-19
TABLE 2103.7(1) – TABLE 2103.7(2)
MASONRY
TABLE 2103.7(1)
MORTAR PROPORTIONS
PROPORTIONS BY VOLUME (cementitious materials)
MORTAR
TYPE
Portland cementa
or blended
cementb
Cement-lime
M
S
N
O
1
1
1
1
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1
/4
over 1/4 to 1/2
over 1/2 to 11/4
over 11/4 to 21/2
Mortar
cement
M
M
S
S
N
O
1
¾
1
/2
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1
—
—
—
—
—
—
—
1
—
—
1
—
1
—
1
1
—
—
—
—
—
—
Masonry
cement
M
M
S
S
N
O
1
—
1/
2
—
—
—
—
1
—
—
—
—
—
—
—
1
—
—
1
—
1
—
1
1
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
a.
b.
c.
d.
e.
Masonry cementc
Mortar cementd
M
S
N
M
S
N
HYDRATED LIMEe
OR LIME PUTTY
AGGREGATE MEASURED
IN A DAMP, LOOSE
CONDITION
Not less than 21/4 and
not more than 3 times
the sum of the separate
volumes of
cementitious materials
Portland cement conforming to the requirements of ASTM C 150.
Blended cement conforming to the requirements of ASTM C 595.
Masonry cement conforming to the requirements of ASTM C 91.
Mortar cement conforming to the requirements of ASTM C 1329.
Hydrated lime conforming to the requirements of ASTM C 207.
TABLE 2103.7(2)
MORTAR PROPERTIESa
MORTAR
TYPE
AVERAGE COMPRESSIVEb
STRENGTH AT 28 DAYS
minimum (psi)
Cement-lime
M
S
N
O
2,500
1,800
750
350
75
75
75
75
12
12
14c
14c
Mortar
cement
M
S
N
O
2,500
1,800
750
350
75
75
75
75
12
12
14c
14c
Masonry
cement
M
S
N
O
2,500
1,800
750
350
75
75
75
75
18
18
20d
20d
WATER RETENTION
minimum (%)
AIR CONTENT
maximum (%)
For SI:
1 inch = 25.4 mm, 1 pound per square inch = 6.895 kPa.
a. This aggregate ratio (measured in damp, loose condition) shall not be less than 21/4 and not more than 3 times the sum of the separate volumes of cementitious materials.
b. Average of three 2-inch cubes of laboratory prepared mortar, in accordance with ASTM C 270.
c. When structural reinforcement is incorporated in cement-lime or mortar cement mortars, the maximum air content shall not exceed 12 percent.
d. When structural reinforcement is incorporated in masonry cement mortar, the maximum air content shall not exceed 18 percent.
21-20
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2103.9.1 Dry-set portland cement mortars. Premixed prepared portland cement mortars, which require only the addition
of water and are used in the installation of ceramic tile, shall
comply with ANSI A118.1. The shear bond strength for tile set
in such mortar shall be as required in accordance with ANSI
A118.1. Tile set in dry-set portland cement mortar shall be installed in accordance with ANSI A108.5.
v Dry-set portland cement mortar for ceramic tile is required to comply with ANSI A118.1, which describes
test methods and minimum requirements for dry-set
mortar, including sampling, free water content, setting
characteristics, shrinkage, shear strength and staining.
Dry-set mortar is a mixture of portland cement, sand
and perhaps water-retention admixtures. Dry-set mortars are suitable for use over properly prepared backings of clay or concrete masonry; concrete; cut-cell expanded polystyrene or rigid closed-cell urethane
insulation board; gypsum wallboard; lean portland cement mortar and hardened wall and floor setting beds.
Installation must comply with ANSI A108.5. The
“thin-bed” mortars are applied in a single layer as thin as
3/
1
1
32 inch (2.4 mm), but usually in thicknesses of /8 to /4
inch (3.2 to 6.4 mm). The use of dry-set mortar for leveling work is limited to a maximum thickness of 1/4 inch
(6.4 mm).
This material has excellent water and impact resistance. It is also water-cleanable, nonflammable, good for
exterior use and requires no presoaking of the tile. Dry-set
mortar is intended for use with glazed wall tile, ceramic
mosaics, pavers and quarry tile.
Shear bond strength (of tile set in mortar) is required
to be tested in accordance with standards applicable to
the mortar used. Tile set with dry-set mortar must be installed in accordance with ANSI A108.5.
2103.9.2 Electrically conductive dry-set mortars. Premixed
prepared portland cement mortars, which require only the addition of water and comply with ANSI A118.2, shall be used in the
installation of electrically conductive ceramic tile. Tile set in
electrically conductive dry-set mortar shall be installed in accordance with ANSI A108.7.
v Mortars used in the installation of electrically conductive
ceramic tile are required to conform to ANSI A108.7 for
premixed prepared mortars and to ANSI A108.7 for conductive dry-set mortars. ANSI A108.7 is the correct reference for tile set in conductive dry-set mortar.
2103.9.3 Latex-modified portland cement mortar. Latex-modified portland cement thin-set mortars in which latex is
added to dry-set mortar as a replacement for all or part of the
gauging water that are used for the installation of ceramic tile
shall comply with ANSI A118.4. Tile set in latex-modified portland cement shall be installed in accordance with ANSI A108.5.
v Latex-modified portland cement mortar is a mixture of
portland cement, sand and special latex admixtures. It
is applied as a thin-bed material, like dry-set portland
cement mortar (see commentary, Section 2103.9.1).
Since the latex used in these mortars varies among
manufacturers, instructions for mixing and use must be
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2103.9.1 – 2103.9.6
followed carefully. Applicable material and installation
standards are ANSI A108.5 and A118.4.
2103.9.4 Epoxy mortar. Ceramic tile set and grouted with
chemical-resistant epoxy shall comply with ANSI A118.3. Tile
set and grouted with epoxy shall be installed in accordance with
ANSI A108.6.
v Epoxy mortar is a two-part system consisting of epoxy
resin and hardener. It is applied as a layer of 1/16 to 1/8
inch (1.6 to 3.2 mm) in thickness and is suitable for use
on properly prepared floors of concrete, wood, plywood,
steel plate or ceramic tile. It is particularly suitable
where chemical resistance or high bond strength is required. Deflection control is critical for the successful
use of this material, and floor systems should not deflect
more than 1/360 of their span. Epoxy mortar is recommended for setting ceramic mosaics, quarry tile and
paver tile. Applicable material and installation standards
are ANSI A108.6 and A118.3.
2103.9.5 Furan mortar and grout. Chemical-resistant furan
mortar and grout that are used to install ceramic tile shall comply with ANSI A118.5. Tile set and grouted with furan shall be
installed in accordance with ANSI A108.8.
v Furan mortar is a two-part system consisting of a furan
resin and a hardener. It is suitable where chemical resistance is critical. It is used primarily on floors in laboratories and industrial plants. Acceptable subfloors include concrete, steel plate and ceramic tile. Furan grout
is intended for quarry tile and pavers, mainly in industrial areas requiring maximum chemical resistance.
ANSI A118.5 is the standard regulating both furan
mortar and grout. Installation must comply with ANSI
A108.8.
2103.9.6 Modified epoxy-emulsion mortar and grout. Modified epoxy-emulsion mortar and grout that are used to install
ceramic tile shall comply with ANSI A118.8. Tile set and
grouted with modified epoxy-emulsion mortar and grout shall
be installed in accordance with ANSI A108.9.
v Modified epoxy-emulsion mortar and grout used to install ceramic tile are required to comply with ANSI
A118.8 and to be installed in accordance with ANSI
A108.9.
ANSI A118.8 describes the test methods and the minimum requirements for modified epoxy-emulsion mortar
and grout. The chemical and solvent resistance of these
mortars and grouts tends to exceed those of organic adhesives and equal those of latex-modified portland-cement mortars. They are not, however, designed to meet
the requirements of ANSI A108.6 or A118.3.
These types of mortars and grouts are three-part systems that include emulsified epoxy resins and hardeners, preblended portland cement and silica sand. They
are used as a bond-coat setting mortar or grout. They
can be cleaned from wall and floor surfaces using a wet
sponge prior to initial set.
ANSI A118.8 regulates water absorption, flexural
21-21
2103.9.7 – 2103.11.1
strength, thermal expansion, linear shrinkage, tensile
strength and compressive strength.
2103.9.7 Organic adhesives. Water-resistant organic adhesives
used for the installation of ceramic tile shall comply with ANSI
A136.1. The shear bond strength after water immersion shall not
be less than 40 psi (275 kPa) for Type I adhesive, and not less
than 20 psi (138 kPa) for Type II adhesive, when tested in accordance with ANSI A136.1. Tile set in organic adhesives shall be
installed in accordance with ANSI A108.4.
v Organic adhesives are prepared materials that cure or set
by evaporation and that are ready to use without adding
liquid or powder. Adhesives are suitable for installing tiles
on prepared wall and floor surfaces, including: brick and
concrete masonry; concrete; gypsum wallboard; portland
cement or gypsum plaster and wood-flooring systems.
Organic adhesives (mastics) are applied as a thin layer
approximately 1/16 inch (1.6 mm) thick. An underlayment
is used to level and true surfaces. Organic adhesive
does not permit the soaking of tiles and is not suitable
for exterior use. Bond strength varies greatly among the
numerous brands of organic adhesives available for
use in construction. Adhesives must meet minimum
bond-strength requirements of this section of ANSI
A136.1 for Type I and II adhesive. The installation of tile
with organic adhesives is required to conform to ANSI
A108.4.
2103.9.8 Portland cement grouts. Portland cement grouts used
for the installation of ceramic tile shall comply with ANSI
A118.6. Portland cement grouts for tile work shall be installed
in accordance with ANSI A108.10.
v Portland cement grouts are the most commonly used
grouts for tile walls. The mixture of portland cement and
other ingredients is water resistant and uniform in color.
The water in the grout is essential to promote a good
bond and to develop full grout strength. This type of
grout is required to comply with ANSI A118.6 and to be
installed in accordance with ANSI A108.10.
2103.10 Grout. Grout shall conform to Table 2103.10 or to
ASTM C 476. When grout conforms to ASTM C 476, the grout
shall be specified by proportion requirements or property requirements.
v Grout intended for use in the construction of engineered
and empirically designed masonry structures is required to comply with ASTM C 476, which regulates materials, measurement, mixing and storage of materials.
Two types of grout are used in masonry: fine and
coarse. Fine grout is made of cement, sand and water,
with optional small quantities of lime. Coarse grout includes the same ingredients, plus pea gravel or a larger
3
/4-inch (19.1 mm) coarse aggregate.
Whether fine or coarse grout is used depends on the
size of the grout space to be filled. Coarse grout is permitted to be used in cavities that are 2 inches (51 mm) or
more in width and in the cells of hollow units that are 4
inches (102 mm) or more in both directions. Smaller
21-22
MASONRY
spaces require the use of fine grout.
The materials used in masonry grout are required to be
listed in ASTM C 476 and must conform to the following
standard specifications: ASTM C 5; ASTM C 150; ASTM
C 207; ASTM C 404 and ASTM C 595.
Grout may be specified either by proportion or property.
When the proportion method is specified, Table 2103.10
provides required proportions of grout materials by volume. Information on property requirements is given in
ASTM C 476.
TABLE 2103.10
GROUT PROPORTIONS BY VOLUME FOR
MASONRY CONSTRUCTION
TYPE
PARTS BY
VOLUME OF
PARTS BY
PORTLAND
VOLUME OF
CEMENT OR HYDRATED
BLENDED LIME OR LIME
PUTTY
CEMENT
AGGREGATE, MEASURED IN A
DAMP, LOOSE CONDITION
Fine
Coarse
0-1/10
2 /4-3 times the
sum of the
volumes of the
cementitious
materials
—
0-1/10
21/4-3 times the
sum of the
volumes of the
cementitious
materials
1-2 times the
sum of the
volumes of the
cementitious
materials
1
Fine
grout
Coarse
grout
1
1
v This table, which is based on ASTM C 476, prescribes
volume proportions of grout for masonry. Information on
fine and coarse grout is given in the commentary to ACI
530.1/ASCE 6/TMS 602. Additionally, ACI 530.1/ASCE
6/TMS 602 provides specific requirements as to where
fine and coarse grout are permitted to be used.
2103.11 Metal reinforcement and accessories. Metal reinforcement and accessories shall conform to Sections 2103.11.1
through 2103.11.7.
v This section contains standards and material requirements for anchors, joint reinforcement, wire accessories, ties, wire fabric and for required corrosion protection of these items.
Several referenced standards originally applied to
steel reinforcement for concrete, but are suitable and
required for masonry construction as well.
2103.11.1 Deformed reinforcing bars. Deformed reinforcing
bars shall conform to one of the following standards: ASTM A
615 for deformed and plain billet-steel bars for concrete reinforcement; ASTM A 706 for low-alloy steel deformed bars for
concrete reinforcement; ASTM A 767 for zinc-coated reinforcing steel bars; ASTM A 775 for epoxy-coated reinforcing steel
bars and ASTM A 996 for rail steel and axle steel deformed bars
for concrete reinforcement.
v ASTM A 615 regulates the manufacture of plain and deformed reinforcement, Grades 40 and 60, for new or recycled steel.
ASTM A 706 regulates the manufacture of plain and
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
deformed reinforcement, Grade 60 only, from mold-cast
or strand-cast steel. This steel is intended for welding, in
accordance with the procedures of AWS D1.4. It is more
ductile than other steel and is especially suitable for
structures in zones of high seismicity (see commentary,
Section 2108.3).
Where masonry is expected to be exposed to especially
corrosive conditions, galvanized reinforcement meeting
ASTM A 767 or epoxy-coated reinforcement meeting
ASTM A 775 can be used.
ASTM A 996 regulates rail steel and axle steel deformed bars.
Deformed reinforcement is recommended for nearly every application in reinforced masonry and is required in
most instances.
2103.11.2 Joint reinforcement. Joint reinforcement shall comply with ASTM A 951. The maximum spacing of crosswires in
ladder-type joint reinforcement and of point of connection of
cross wires to longitudinal wires of truss-type reinforcement
shall be 16 inches (400 mm).
v ASTM A 951 contains material requirements, mechanical properties and tolerances for joint reinforcement.
Longitudinal wires are required to be deformed in accordance with this standard to provide a mechanical bond
with the surrounding mortar. Cross wires are plain.
ASTM A 82 regulates the manufacture of cold-drawn,
plain steel wire for joint reinforcement, wire anchors and
ties. Joint reinforcement can be epoxy coated to provide
added corrosion protection (see commentary, Section
2103.11.6).
2103.11.2 – 2103.11.6
strip and ASTM A 366 for cold-rolled carbon steel sheet, commercial quality.
v Anchors, ties and accessories are manufactured in a
variety of ways with a number of materials. Applicable
ASTM specifications prescribe minimum requirements
for these materials.
ASTM A 36 regulates the manufacture of hot-rolled
steel with a minimum specified yield stress of 36 ksi
(248 MPa), for general structural purposes. This material is suitable for welding.
ASTM A 82 regulates the manufacture of cold-drawn,
plain-steel wire for joint reinforcement, wire anchors
and ties.
ASTM A 185 regulates the manufacture of plain-steel
welded-wire fabric, using ASTM A 82 steel, or ASTM A
167 Type 304, corrosion-resistant steel.
ASTM A 366 regulates the manufacture of sheet steel
used for metal anchors and ties. The specification covers
cold-rolled carbon steel sheet of commercial quality, in
coils or cut lengths. This material is intended for exposed
or unexposed parts made by bending, moderate drawing,
forming or welding. This standard also specifies mechanical properties and tests relative to bending, hardness and
moderate deformability and sets requirements for chemical composition. See Figure 2109.6.3(1) for typical masonry accessories.
2103.11.6 Prestressing tendons. Prestressing tendons shall
conform to one of the following standards:
a. Wire . . . . . . . . . . ASTM A 421
b. Low-relaxation wire . . ASTM A 421
2103.11.3 Deformed reinforcing wire. Deformed reinforcing
wire shall conform to ASTM A 496.
v ASTM A 496 regulates the manufacture of cold-worked,
deformed wire having yield stresses of 70 ksi (483 MPa)
(welded wire fabric) and 75 ksi (517 MPa). This wire is
used as reinforcement and in the manufacture of
welded, deformed-wire fabric. It is not commonly used
in masonry.
2103.11.4 Wire fabric. Wire fabric shall conform to ASTM A
185 for plain steel-welded wire fabric for concrete reinforcement or ASTM A 496 for welded deformed steel wire fabric for
concrete reinforcement.
v ASTM A 185 regulates the manufacture of plain
welded-wire fabric, using ASTM A 82 steel. ASTM A
497 regulates the manufacture of welded deformed wire
fabric using steels conforming to ASTM A 82 and A 496,
alone or in combination. Wire fabric is seldom used in
masonry.
2103.11.5 Anchors, ties and accessories. Anchors, ties and accessories shall conform to the following standards: ASTM A 36
for structural steel; ASTM A 82 for plain steel wire for concrete
reinforcement; ASTM A 185 for plain steel-welded wire fabric
for concrete reinforcement; ASTM A 167, Type 304, for stainless and heat-resisting chromium-nickel steel plate, sheet and
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
c. Strand . . . . . . . . . ASTM A 416
d. Low-relaxation strand. . ASTM A 416
e. Bar . . . . . . . . . . . ASTM A 722
Exceptions:
1. Wire, strands and bars not specifically listed in ASTM
A 421, ASTM A 416 or ASTM A 722 are permitted,
provided they conform to the minimum requirements
in ASTM A 421, ASTM A 416, or ASTM A 722 and
are approved by the architect/engineer.
2. Bars and wires of less than 150 kips per square inch
(ksi) (1034 MPa) tensile strength and conforming to
ASTM A 82, ASTM A 510, ASTM A 615, ASTM A
616, ASTM A 996 or ASTM A 706/A 706 M are permitted to be used as prestressed tendons provided that:
2.1. The stress relaxation properties have been assessed by tests according to ASTM E 328 for
the maximum permissible stress in the tendon.
2.2. Other nonstress-related requirements of ACI
530/ASCE 5/TMS 402, Chapter 4, addressing
prestressing tendons are met.
v This section specifies the materials for components of
the prestressing system. They are similar to those used
in prestressed concrete.
21-23
2103.11.7 – 2104.1
2103.11.7 Corrosion protection. Corrosion protection for
prestressing tendons, prestressing anchorages, couplers and end
block shall comply with the requirements of ACI 530.1/ASCE
6/TMS 602, Article 2.4G. Corrosion protection for carbon steel
accessories used in exterior wall construction or interior walls
exposed to a mean relative humidity exceeding 75 percent shall
comply with either Section 2103.11.7.1 or 2103.11.7.2. Corrosion protection for carbon steel accessories used in interior walls
exposed to a mean relative humidity equal to or less than 75 percent shall comply with either Section 2103.11.7.1, 2103.11.7.2
or 2103.11.7.3.
v Joint reinforcement, anchors, wall ties and accessories
are required to be galvanized to protect the steel from
deterioration and corrosion, unless the steel is inherently corrosion resistant, such as ASTM A 167 Type 304
stainless steel. The application and thickness of the galvanizing depends on the intended location or severity of
exposure. Carbon steel accessories located in exterior
masonry wall construction are required to be either
hot-dipped galvanized in accordance with Section
2103.11.7.1 or epoxy coated in accordance with Section
2103.11.7.2. Carbon steel accessories for use in interior-wall construction are permitted to comply with
less-restrictive mill galvanized requirements as noted in
Section 2103.11.7.3.
2103.11.7.1 Hot-dipped galvanized. Apply a hot-dipped galvanized coating after fabrication as follows:
1. For joint reinforcement, wall ties, anchors and inserts, apply a minimum coating of 1.5 ounces per square foot (psf)
(458 g/m2) complying with the requirements of ASTM A
153, Class B.
2. For sheet metal ties and sheet metal anchors, comply with
the requirements of ASTM A 153, Class B.
3. For steel plates and bars, comply with the requirements of
either ASTM A 123 or ASTM A 153, Class B.
v Carbon steel accessories located in exterior masonry
wall construction are required to meet the protection requirements of ASTM A 153, which regulates
zinc-coated iron and steel hardware. The minimum required coating of 1.5 ounces per square foot of surface
(458 g/m2) is derived from Table 1 of ASTM A 153 for
rolled, pressed and forged articles under 3/16 inch (4.8
mm) in thickness and over 15 inches (381 mm) in
length.
The finish and appearance of zinc-coated articles are
specified in ASTM A 153. Zinc-coated articles are required to be free from uncoated areas, blisters, flux deposits, black spots and other inclusions that would interfere with the intended use. The coating is required to be
smooth and uniform in thickness.
2103.11.7.2 Epoxy coatings. Carbon steel accessories shall be
epoxy coated as follows:
1. For joint reinforcement, comply with the requirements of
ASTM A 884 Class B, Type 2 – 18 mils (457µm).
2. For wire ties and anchors, comply with the requirements
of ASTM A 899 Class C —20 mils (508µm).
21-24
MASONRY
3. For sheet metal ties and anchors, provide a minimum
thickness of 20 mils (508µm) or in accordance with the
manufacturer’s specification.
v As an alternative to hot-dipped galvanizing, carbon
steel accessories in exterior walls can be epoxy coated.
This section specifies the appropriate coating type and
minimum coating thickness applicable to each type of
accessory.
2103.11.7.3 Mill galvanized. Apply a mill galvanized coating
as follows:
1. For joint reinforcement, wall ties, anchors and inserts, apply a minimum coating of 0.1 ounce psf (31g/m2) complying with the requirements of ASTM A 641.
2. For sheet metal ties and sheet metal anchors, apply a minimum coating complying with Coating Designation G-60
according to the requirements of ASTM A 653.
3. For anchor bolts, steel plates or bars not exposed to the
earth, weather or a mean relative humidity exceeding 75
percent, a coating is not required.
v Carbon steel accessories for use in interior-wall construction are permitted to comply with less-restrictive
material specifications (ASTM A 641), as noted.
2103.11.8 Tests. Where unidentified reinforcement is approved
for use, not less than three tension and three bending tests shall
be made on representative specimens of the reinforcement from
each shipment and grade of reinforcing steel proposed for use in
the work.
v Reinforcing bars are to be rolled with raised symbols or
letters impressed on the metal identifying the manufacturing mill. When required by the building official, the
grade of material is to be identified by a satisfactory mill
test. When the manufacturing mill is not identified but
the reinforcement is approved for use under ordinary
material procedures, at least three tension and three
bending tests are required on representative specimens
of the reinforcement from each shipment and grade of
reinforcing steel proposed for use. The tension and
bending tests are required to be performed by an approved testing agency.
SECTION 2104
CONSTRUCTION
2104.1 Masonry construction. Masonry construction shall
comply with the requirements of Sections 2104.1.1 through
2104.5 and with ACI 530.1/ASCE 6/TMS 602.
v This section establishes the requirements, based on accepted practice and referenced standards, regulating
materials and construction methods used in engineered
and empirically designed masonry construction. Engineered masonry construction is further regulated by
Sections 2101.2.1 and 2101.2.2.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2104.1.1 – FIGURE 2104.1.2.1.1
2104.1.1 Tolerances. Masonry, except masonry veneer, shall be
constructed within the tolerances specified in ACI 530.1/ASCE
6/TMS 602.
v The MSJC Specification, ACI 530.1/ASCE 6/TMS 602,
prescribes tolerances for placement of reinforcement
and masonry units. Specific tolerances listed include
cross sections of elements; thicknesses of mortar joints;
widths of grout spaces; variation from level; variation
from plumb; trueness to a line; alignment of columns
and walls; location of elements and placement of reinforcement and accessories. These required tolerances
are intended to inhibit corrosion; provide placement locations reflecting those assumed in design; provide
clearance for mortar and grout and maintain compatible
lateral deflections of parallel wythes. Tolerances are relatively strict since masonry is a structural material and
is also exposed to weather. Aesthetics are not a factor in
these requirements.
2104.1.2 Placing mortar and units. Placement of mortar and
units shall comply with Sections 2104.1.2.1 through 2104.1.2.5.
v Workmanship is of primary importance in providing strong
and durable masonry construction. This is especially true
for the placement of mortar and masonry unit. Water penetration can often be traced to bond breaks at the mortar-unit interface. Additionally, masonry strength relies on
the mortar bedded areas required in this section and ACI
530.1/ASCE 6/TMS 602.
2104.1.2.1 Bed and head joints. Unless otherwise required or
indicated on the construction documents, head and bed joints
shall be 3/8 inch (9.5 mm) thick, except that the thickness of the
bed joint of the starting course placed over foundations shall not
be less than 1/4 inch (6.4 mm) and not more than 3/4 inch (19.1
mm).
v The required thickness for bed joints has a permitted tolerance of plus or minus 1/8 inch (3 mm). This thickness is intended to provide bonding of reinforcement and ties and
to allow for the dimensional tolerances of the masonry
units. The greater permitted thickness of the starting
mortar course is intended to accommodate variations in
the elevation of the top surface of the foundation.
2104.1.2.1.1 Open-end units. Open-end units with beveled
ends shall be fully grouted. Head joints of open-end units with
beveled ends need not be mortared. The beveled ends shall form
a grout key that permits grouts within 5/8 inch (15.9 mm) of the
face of the unit. The units shall be tightly butted to prevent leakage of the grout.
v Open-end units can be placed around vertical reinforcing steel, rather than having to be lifted up and over it, as
closed-end units must be. Such units are manufactured
with one or no end shells.
The special type of open-end unit described in this
section is manufactured with beveled ends of the
faceshells, so that when the unit is grouted, grout fills
the head joint seam (see Figure 2104.1.2.1.1). Because
of this, head joints of such construction need not be
filled with mortar. Open-end units without this bevel
must be laid with mortared head joints.
Figure 2104.1.2.1.1
MORTARLESS HEAD JOINT UNIT
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-25
2104.1.2.2 – 2104.1.2.4
MASONRY
2104.1.2.2 Hollow units. Hollow units shall be placed such that
face shells of bed joints are fully mortared. Webs shall be fully
mortared in all courses of piers, columns, pilasters, in the starting course on foundations where adjacent cells or cavities are to
be grouted, and where otherwise required. Head joints shall be
mortared a minimum distance from each face equal to the face
shell thickness of the unit.
v Figure 2104.1.2.2 shows the typical placement of mortar
for hollow-unit masonry walls. Except for the initial bed
joint at the starter course, the cross webs of hollow units in
walls are not usually mortared except at the cross webs of
cells that are to be grouted in partially grouted walls. Cross
webs of hollow units in piers, columns and pilasters, however, are required to be mortared.
2104.1.2.3 Solid units. Unless otherwise required or indicated
on the construction documents, solid units shall be placed in
fully mortared bed and head joints. The ends of the units shall be
completely buttered. Head joints shall not be filled by slushing
with mortar. Head joints shall be constructed by shoving mortar
tight against the adjoining unit. Bed joints shall not be furrowed
deep enough to produce voids.
v Solid units result in fully mortared bed joints since the
25-percent core area is effectively crossed with mortar.
Height-to-thickness ratios and calculated stresses are
based on the fully mortared bed joint.
Filling head joints by slushing from above is not permitted, since this could result in voids and lead to water
penetration. The head-joint mortar may be placed on
the end of the masonry unit prior to placing the unit in
the wall. The furrow typically formed during bed joint
placement should not be too deep since mortar voids
would result (see Figure 2104.1.2.3).
2104.1.2.4 Glass unit masonry. Glass units shall be placed so
head and bed joints are filled solidly. Mortar shall not be furrowed.
Unless otherwise required, head and bed joints of glass unit
masonry shall be 1/4 inch (6.4 mm) thick, except that vertical
joint thickness of radial panels shall not be less than 1/8 inch (3.2
mm). The bed joint thickness tolerance shall be minus 1/16 inch
(1.6 mm) and plus 1/8 inch (3.2 mm). The head joint thickness
tolerance shall be plus or minus 1/8 inch (3.2 mm).
v Glass unit masonry is required to be placed with full
head and bed joints. Glass units are manufactured to be
modular with a joint thickness of 1/4 inch (6.4 mm),
smaller than the typical 3/8 inch (9.6 mm) for concrete
masonry and the 3/8 inch (9.6 mm) or 1/2 inch (12.8 mm)
joint thickness for clay brick masonry. Designers should
recognize this difference and use correct nominal dimensions when laying out glass unit masonry.
Tolerances for glass unit masonry are much tighter
than for other types of masonry because glass unit masonry units are manufactured to very tight tolerances
and are more dimensionally stable than other types of
masonry.
Head joints on radial panels of glass unit masonry are
permitted to be as thin as 1/8 inch (3.2 mm), because
placing rectangular units in a curved wall requires wider
joints on one face of the wall and narrower joints on the
other face.
HEAD JOINTS
BED JOINTS
Figure 2104.1.2.2
MORTAR PLACEMENT ON HOLLOW UNITS IN WALLS
21-26
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2104.1.2.5 – 2104.1.3
FURROW
NO VOIDS WHEN
BRICK REMOVED
ACCEPTABLE
VOIDS WHEN
BRICK REMOVED
UNACCEPTABLE
Figure 2104.1.2.3
FURROWING
2104.1.2.5 All units. Units shall be placed while the mortar is
soft and plastic. Any unit disturbed to the extent that the initial
bond is broken after initial positioning shall be removed and
relaid in fresh mortar.
v Mortar should not be spread too far ahead of units, as it
will stiffen and lose plasticity, especially in hot weather.
Mortar that has stiffened should not be used. ASTM C
270 requires that mortar be used within 2½ hours of initial mixing.
A test for mortar workmanship includes removal of a
unit. Bonded mortar will stick to the removed unit as well
as the remaining masonry; stiff, unbonded mortar will
not. Broken joints should be remortared.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2104.1.3 Installation of wall ties. The ends of wall ties shall be
embedded in mortar joints. Wall tie ends shall engage outer face
shells of hollow units by at least 1/2 inch (12.7 mm). Wire wall
ties shall be embedded at least 11/2 inches (38 mm) into the mortar bed of solid masonry units or solid-grouted hollow units.
Wall ties shall not be bent after being embedded in grout or mortar.
v Installation of wall ties requires adequate embedment in
mortar, adequate strength and durability of ties. Wall
ties are not permitted to be bent after being embedded
in grout or mortar, since movement of the ties will reduce the effectiveness of the embedment and subsequent bonding.
21-27
2104.1.4 – 2104.2
2104.1.4 Chases and recesses. Chases and recesses shall be
constructed as masonry units are laid. Masonry directly above
chases or recesses wider than 12 inches (305 mm) shall be supported on lintels.
v Chases and recesses are designed so that they do not
reduce the required strength of the walls or affect the required fire-resistance rating of the wall. Any required
chases must be formed during construction of the masonry wall and not by cutting out a section of the finished
wall, which could create a weak point and jeopardize
the wall strength.
This empirical limitation requires lintels for chases
and recesses wider than 12 inches (305 mm). Although
arching action reduces lintel moments, the potential of
weaknesses created by chases and recesses makes
them subject to engineered design. The supporting lintel is permitted to be of masonry, concrete or steel and
must be engineered as required in Section 2104.1.5.
2104.1.5 Lintels. The design for lintels shall be in accordance
with the masonry design provisions of either Section 2107 or
2108. Minimum length of end support shall be 4 inches (102
mm).
v Masonry lintels are required to be engineered as
load-bearing beam elements by either the working
stress design method of Section 2107 or the strength
design method of Section 2108. This requirement is
consistent with the empirical provisions, which do not include horizontally spanning elements such as beams.
Bearing on masonry is required to be a minimum of 4
inches (102 mm) to adequately distribute stresses.
2104.1.6 Support on wood. Masonry shall not be supported on
wood girders or other forms of wood construction except as permitted in Section 2304.12.
v Masonry is not permitted to be supported on wood construction, except as permitted in Section 2304.12, because of both the danger of collapse in case of fire and
the serviceability considerations noted below.
Masonry is brittle and relatively weak in tension. It can
crack when subjected to deformations. Wood is flexible
and usually exhibits elastic deformation and creep (additional deflection from long-term loads). Because of
this, masonry supported on wood tends to crack. Therefore, masonry is not permitted to be supported by wood
members, unless such masonry meets the exceptions
in Section 2304.12.
Glass-block panels are typically limited in size and
are often used in windows as decoration. For this limited
use, support on wood is permitted. The deflection limitation in Section 2110.4.2 is consistent with the requirements for masonry. In calculating the probable deflection of the supporting wood member, consideration of
creep is recommended.
2104.1.7 Masonry protection. The top of unfinished masonry
work shall be covered to protect the masonry from the weather.
21-28
MASONRY
v Water can accumulate within masonry walls and it evaporates relatively slowly. Moisture migrates to the surface, dissolves salts in the masonry and deposits them
on the surface as a white powder called “efflorescence.”
To prevent this, the tops of walls exposed to weather are
required to be covered.
2104.1.8 Weep holes. Weep holes provided in the outside wythe
of masonry walls shall be at a maximum spacing of 33 inches
(838 mm) on center (o.c.). Weep holes shall not be less than 3/16
inch (4.8 mm) in diameter.
v Masonry is not water tight. Water can penetrate into and
through it. Weep holes are to be provided in all masonry
wall construction to help water leave the wall. Without
weep holes, moisture would remain within the masonry
construction and evaporation would be its only means
of exit.
Many methods for providing weep holes are available, including open head joints; 3/8-inch-diameter (9.6
mm) holes in joints and wicking cord laid in the joint and
behind the brick.
The 33-inch (838 mm) maximum spacing of weep
holes, while apparently odd since it is not modular for
typical masonry, was selected because weep holes are
often spaced at 32 inches (813 mm) on center, plus or
minus typical construction tolerances.
2104.2 Corbeled masonry. The maximum corbeled projection
beyond the face of the wall shall not be more than one-half of the
wall thickness nor one-half the wythe thickness for hollow
walls. The maximum projection of one unit shall neither exceed
one-half the height of the unit nor one-third the thickness at right
angles to the wall.
v This section covers the limitations and the construction
features of corbeled masonry.
A corbel is formed by projecting courses of masonry
with the first or lowest course projecting out from the
face of the wall and each successive course projecting
out from the supporting course below. While corbels
may be constructed using various load-bearing masonry units, they are most commonly applied to clay
masonry and are used for aesthetic purposes and to
support offset or thickened walls above them.
The permitted extent of corbeling is illustrated in Figure 2104.2. The total horizontal projection of a corbel
from the face of the wall is limited to no more than
one-half the wall thickness of a solid wall or more than
one-half the thickness of the wythe in a cavity wall. Furthermore, the projection of a single course is not to exceed one-half of the unit height, nor one-third of the unit
bed depth, whichever is less.
These limitations establish a maximum angle of
corbelled brick masonry, measured from the plane of
the wall, of about 261/2 degrees (0.46 rad). A smaller angle can be achieved by decreasing the brick projections
to less than the maximum allowed by this section.
Corbels produce and often transfer eccentric loads,
which must be considered in the design of masonry
walls.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2104.2.1 – 2104.3.1
Corbels constructed in walls of hollow units or in hollow
masonry walls are required to be of solid masonry. This requirement can be satisfied by using solid units, grouting
the cores of hollow units or grouting open spaces in hollow
walls.
2104.2.1 Molded cornices. Unless structural support and anchorage are provided to resist the overturning moment, the center of gravity of projecting masonry or molded cornices shall lie
within the middle one-third of the supporting wall. Terra cotta
and metal cornices shall be provided with a structural frame of
approved noncombustible material anchored in an approved
manner.
v Figure 2104.2.1 illustrates this requirement. Unless cornices or other projections are specifically designed to be
supported and anchored to the wall or other adequate
structural supports, such as columns, beams, spandrels
or floor slabs, the center of gravity of the projecting element is required to fall within the middle third (kern) of
the supporting wall.
Cornices are usually ornamental and may or may not
support other loads. They can be made of cast-in-place
or precast concrete; cast or natural stone; terra cotta;
brick or even metal.
Metal and terra-cotta cornices are commonly furnished with a structural frame of noncombustible mate-
rial that can be anchored to the masonry wall or to other
building supports as approved by the building official.
2104.3 Cold weather construction. The cold weather construction provisions of ACI 530.1/ASCE 6/TMS 602, Article
1.8 C, or the following procedures shall be implemented when
either the ambient temperature falls below 40°F (4°C) or the
temperature of masonry units is below 40°F (4°C).
v When masonry construction is conducted in temperatures below 40°F (4°C), both the masonry components
and the structure are required to be protected in accordance with this section. One of the main goals of these
provisions is to prevent fresh mortar from freezing.
During cold-weather construction, especially in temperatures below freezing, the curing and subsequent
performance of masonry are influenced by the temperature and properties of the mortar and the masonry units,
as well as the severity of the exposure (temperature and
wind).
2104.3.1 Preparation.
1. Temperatures of masonry units shall not be less than 20°F
(-7°C) when laid in the masonry. Masonry units containing frozen moisture, visible ice or snow on their surface
shall not be laid.
d
LIMITATIONS ON CORBELING:
P < t/2
p < h/2
p < d/3
h
SOLID UNITS REQUIRED
P = ALLOWABLE TOTAL
h
HORIZONTAL PROJECTION
OF CORBELING
p = ALLOWABLE PROJECTION
OF ONE UNIT
p
t = WALL THICKNESS
p
h = UNIT HEIGHT
d = UNIT THICKNESS
FOR h < 2/3d,
LIMITING SLOPE OF CORBELING (
TAN
t
= h/p
Pmax = h/2
P
Tan
For SI:
):
min = 2
> 63E 26'
1 degree = 0.01745 rad.
Figure 2104.2
CORBELED MASONRY
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-29
2104.3.2 – 2104.3.2.1
MASONRY
2. Visible ice and snow shall be removed from the top surface of existing foundations and masonry to receive new
construction. These surfaces shall be heated to above
freezing, using methods that do not result in damage.
v Under cold-weather conditions masonry construction
should not proceed if these requirements are not met.
Masonry units to be used during cold-weather construction should be dry. Masonry must not be laid on snow or
ice-covered surfaces, because bond cannot be developed between the units and the mortar bed under those
conditions. Additionally, the units can move when the
mortar thaws.
2104.3.2 Construction. The following requirements shall apply
to work in progress and shall be based on ambient temperature.
v This section sets minimum requirements to be met as
masonry work proceeds based on the ambient temperature. Mortars (or grout) mixed at low temperatures using cold (not frozen) materials have plastic properties
that are significantly different from those mixed at temperatures above 40°F (4°C). If the water content of the
mortar is more than 6 to 8 percent when it freezes, expansion and possible damage could occur. If the water
content of the mortar is less than 6 to 8 percent, the expected mortar expansion is less severe.
Antifreeze admixtures should not be permitted as a
means of lowering the freezing point of mortar. Simply
keeping the mortar from freezing does not result in
proper hydration. Some commercially available mortar
admixtures that claim to have antifreeze qualities may
be improperly described or labeled because they do not
t/3
RESULTANT
WEIGHT
t/3
significantly lower the freezing point of the mortar, but
rather serve as accelerators of cement hydration. Calcium chloride is the most commonly used accelerator
and is the main ingredient in many commercially available mortar admixtures. Because chlorides enhance
the corrosion of embedded steel, however, admixtures
containing chlorides should not be used in masonry
containing metal ties, joint reinforcement or other metal
accessories in contact with mortar.
Mortar mixed at a low temperature requires longer
curing times and gains strength more slowly than mortar
mixed at higher temperatures. To counteract the slow
strength development of mortar at low temperatures,
mixing water is required to be heated. In some instances, the sand used in the mortar is also heated. To
accelerate early strength development, Type III
(high-early-strength portland cement) can be substituted for Type I cement.
Cold-weather conditions do not require any changes
to the mortar or grout mix proportions of cement, lime
and sand (and coarse aggregate for grout).
2104.3.2.1 Construction requirements for temperatures between 40°F (4°C) and 32°F (0°F). The following construction
requirements shall be met when the ambient temperature is between 40°F (4°C) and 32°F (0°C):
1. Glass unit masonry shall not be laid.
2. Water and aggregates used in mortar and grout shall not be
heated above 140°F (60°C).
3. Mortar sand or mixing water shall be heated to produce
mortar temperatures between 40°F (4°C) and 120°F
t/3
BECAUSE RESULTANT IS NOT
WITHIN MIDDLE THIRD (KERN),
ANCHORAGE IS PROVIDED
CG
CORNICE
(COPING)
COMPOSITE (MONOLITHIC)
MASONRY WALL
t = ACTUAL THICKNESS (WIDTH)
OF SUPPORTING WALL
Figure 2104.2.1
MOLDED CORNICE
21-30
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
(49°C) at the time of mixing. When water and aggregates
for grout are below 32°F(0°C), they shall be heated.
v See the commentary to Section 2104.3.2.
2104.3.2.2 Construction requirements for temperatures between 32°F (0°C) and 25°F (-4°C). The requirements of Section 2104.3.2.1 and the following construction requirements
shall be met when the ambient temperature is between 32°F
(0°C) and 25°F (-4°C):
1. The mortar temperature shall be maintained above freezing until used in masonry.
2. Aggregates and mixing water for grout shall be heated to
produce grout temperature between 70°F (21°C) and
120°F (49°C) at the time of mixing. Grout temperature
shall maintained above 70°F (21°C) at the time of grout
placement.
v See the commentary to Section 2104.3.2.
2104.3.2.3 Construction requirements for temperatures between 25°F (-4°C) and 20°F (-7°C). The requirements of Sections 2104.3.2.1 and 2104.3.2.2 and the following construction
requirements shall be met when the ambient temperature is between 25°F (-4°C) and 20°F (-7°C):
1. Masonry surfaces under construction shall be heated to
40°F (4°C).
2. Wind breaks or enclosures shall be provided when the
wind velocity exceeds 15 miles per hour (mph) (24 km/h).
3. Prior to grouting, masonry shall be heated to a minimum
of 40°F (4°C).
v Low temperatures do not significantly affect the performance characteristics of masonry units. The absorption
(suction) characteristics of cold, wet and frozen masonry units are decreased, however, which may affect
mortar bond. Preheating masonry units prevents the
sudden cooling of warm mortar in contact with cold
units. A heated unit will absorb more water from the
mortar because of the absorptive characteristics of a
cooling body.
In selecting masonry units for cold-weather construction, consideration should be given to the absorption
rates (see ASTM C 67). Units with initial rates of absorption of 30 grams per 30 square inches (19 355 mm2) per
minute are preferable for cold-weather construction because they greatly reduce the possibility of disruptive
expansion of the mortar due to freezing. Units with an
initial rate of absorption of 5 to 6 grams per 30 square
inches (19 355 mm2) per minute or less may not absorb
sufficient water to prevent disruptive expansion if the
mortar freezes (also see commentary, Section
2104.3.2).
2104.3.2.4. Construction requirements for temperatures below 20°F (-7°C). The requirements of Sections 2104.3.2.1,
2104.3.2.2 and 2104.3.2.3 and the following construction re-
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2104.3.2.2 – 2104.3.3.4
quirement shall be met when the ambient temperature is below
20°F (-7°C): Enclosures and auxiliary heat shall be provided to
maintain air temperature within the enclosure to above 32°F
(0°C).
v In addition to all of the above requirements, ambient
temperatures below 20EF (-7EC) require the masonry
construction to be enclosed and the use of auxiliary
heat (also see commentary, Section 2104.3.2).
2104.3.3 Protection. The requirements of this section and Sections 2104.3.3.1 through 2104.3.3.4 apply after the masonry is
placed and shall be based on anticipated minimum daily temperature for grouted masonry and anticipated mean daily temperature for ungrouted masonry.
v This section sets minimum requirements to be met after
masonry work is completed based on the anticipated
temperature. Lower expected temperatures require
more extensive means of protection.
2104.3.3.1 Glass unit masonry. The temperature of glass unit
masonry shall be maintained above 40°F (4°C) for 48 hours after construction.
v See the commentary to Sections 2104.3 and 2104.3.3.
2104.3.3.2 Protection requirements for temperatures between 40°F (4°C) and 25°F (-4°C). When the temperature is
between 40°F (4°C) and 25°F (-4°C), newly constructed masonry shall be covered with a weather-resistive membrane for 24
hours after being completed.
v See the commentary to Sections 2104.3 and 2104.3.3.
2104.3.3.3 Protection requirements for temperatures between 25°F (-4°C) and 20°F (-7°C). When the temperature is
between 25°F (-4°C) and 20°F (-7°C), newly constructed masonry shall be completely covered with weather-resistive insulating blankets, or equal protection, for 24 hours after being
completed. The time period shall be extended to 48 hours for
grouted masonry, unless the only cement in the grout is Type III
portland cement.
v See the commentary to Sections 2104.3 and 2104.3.3.
2104.3.3.4 Protection requirements for temperatures below
20°F (-7°C). When the temperature is below 20°F (-7°C), newly
constructed masonry shall be maintained at a temperature above
32°F (0°C) for at least 24 hours after being completed by using
heated enclosures, electric heating blankets, infrared lamps or
other acceptable methods. The time period shall be extended to
48 hours for grouted masonry, unless the only cement in the
grout is Type III portland cement.
v When temperatures are less than 20°F (-7°C), temporary heating is required to protect the masonry (also see
commentary, Sections 2104.3 and 2104.3.3).
21-31
2104.4 – 2104.5
MASONRY
2104.4 Hot weather construction. The hot weather construction provisions of ACI 530.1/ASCE 6/TMS 602, Article 1.8 D,
or the following procedures shall be implemented when the temperature or the temperature and wind-velocity limits of this section are exceeded.
2. Mixers, mortar transport containers and mortar boards
shall be flushed with cool water before they come into
contact with mortar ingredients or mortar.
v Temperature, solar radiation, humidity and wind influence the rate of absorption of masonry units and the
rate of mortar set. During hot-weather conditions, special precautions must be taken for adequate strength
gain of the masonry.
4. Mortar shall be used within 2 hours of initial mixing.
2104.4.1 Preparation. The following requirements shall be met
prior to conducting masonry work.
v This section imposes minimum required precautions
before masonry work proceeds under hot-weather conditions. The purpose is to maintain mortar temperatures
less than that which causes a flash set.
2104.4.1.1 Temperature. When the ambient temperature exceeds 100°F (38°C), or exceeds 90°F (32°C) with a wind velocity greater than 8 mph (13 km/h):
1. Necessary conditions and equipment shall be provided to
produce mortar having a temperature below 120°F
(49°C).
2. Sand piles shall be maintained in a damp, loose condition.
3. Mortar consistency shall be maintained by retempering
with cool water.
v When hot-weather conditions exceed the limitations of
this section, procedures are required to keep mortar
and grout cool. These procedures include flushing mortar board, containers and other surfaces in contact with
mortar and grout with water and retempering.
2104.4.2.2 Special conditions. When the ambient temperature
exceeds 115°F (46°C), or exceeds 105°F (40°C) with a wind velocity greater than 8 mph (13 km/h), the requirements of Section
2104.4.2.1 shall be implemented and cool mixing water shall be
used for mortar and grout. The use of ice shall be permitted in
the mixing water prior to use. Ice shall not be permitted in the
mixing water when added to the other mortar or grout materials.
v In extreme hot-weather conditions, ice can be added to
the mixing water for mortar and grout to maintain their
temperatures at acceptable levels. Ice cannot, however,
be present in the mixing water when it is added to the
dry materials in the mortar or grout.
v When hot-weather conditions exceed those specified,
procedures are required to keep mortar and sand in an
acceptable condition.
2104.4.3 Protection. When the mean daily temperature exceeds
100°F (38°C), or exceeds 90°F (32°C) with a wind velocity
greater than 8 mph (13 km/h), newly constructed masonry shall
be fog sprayed until damp at least three times a day until the masonry is three days old.
2104.4.1.2 Special conditions. When the ambient temperature
exceeds 115°F (46°C), or 105°F (40°C) with a wind velocity
greater than 8 mph (13 km/h), the requirements of Section
2104.4.1.1 shall be implemented, and materials and mixing
equipment shall be shaded from direct sunlight.
v When hot-weather conditions are extended (as defined by
the mean daily temperature), masonry is required to be
fogsprayed to help hydrate it. Excessive wetting of the
wall, however, can cause adverse effects such as efflorescence and moisture expansion in concrete masonry.
v When hot-weather conditions are extreme, materials
and mixing equipment are required to be shaded, in addition to the requirements in Section 2104.4.1.1. Unshaded equipment becomes so hot that mortar can experience flash set.
2104.4.2 Construction. The following requirements shall be
met while masonry work is in progress.
v This section imposes minimum precautions to be taken
as masonry work proceeds under hot-weather conditions. Their purpose is to keep mortar temperatures
lower than that which causes flash set. Ice is prohibited
because of the potential for weak mortar and grout.
2104.4.2.1 Temperature. When the ambient temperature exceeds 100°F (38°C), or exceeds 90°F (32°C) with a wind velocity greater than 8 mph (13 km/h):
1. The temperature of mortar and grout shall be maintained
below 120°F (49°C).
21-32
2104.5 Wetting of brick. Brick (clay or shale) at the time of laying shall require wetting if the unit’s initial rate of water absorption exceeds 30 grams per 30 square inches (19 355 mm2) per
minute or 0.035 ounce per square inch (1 g/645 mm2) per
minute, as determined by ASTM C 67.
v Clay brick laid on fresh mortar generally absorbs water
from the mortar along with fine particles of cementitious
materials, which help to bond the mortar with the brick. If
the brick absorbs too much water, the mortar may have
insufficient water for hydration. It is therefore necessary
to determine the initial rate of absorption (IRA) of the
brick.
Mortar bonds best with brick whose IRA is between 5
and 30 grams per 30 square inches (19 355 mm2) of
surface per minute. Where the water absorption rate exceeds 30 grams per 30 square inches (19 355 mm2) per
minute (as determined by ASTM C 67), brick is required
to be wetted before placement, but should be surface
dry when laid.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2105 – TABLE 2105.2.2.1.1
SECTION 2105
QUALITY ASSURANCE
2105.1 General. A quality assurance program shall be used to
ensure that the constructed masonry is in compliance with the
construction documents.
v There are two means of determining the compressive
strength of masonry: the unit strength method and the
prism test method. The first eliminates the expense of
prism tests, but is more conservative.
2105.2.2.1 Unit strength method.
v This section requires that a quality assurance program
be used so that the masonry is constructed according to
the contract documents. In addition, inspection and
testing complying with Chapter 17 also requires verification of the masonry compressive strength.
The quality assurance program shall comply with the
inspection and testing requirements of Chapter 17.
v This section describes a prescriptive procedure to estimate the expected compressive strength of the masonry based on the compressive strength of masonry
units and the mortar type. This so-called unit strength
method was generated using prism test data. Mortar
joint thickness is limited because it influences the compressive strength of masonry.
2105.2 Acceptance relative to strength requirements.
2105.2.2.1.1 Clay masonry. The compressive strength of masonry shall be determined based on the strength of the units and
the type of mortar specified using Table 2105.2.2.1.1, provided:
1. Units conform to ASTM C 62, ASTM C 216 or ASTM C
652 and are sampled and tested in accordance with ASTM
C 67.
2. Thickness of bed joints does not exceed 5/8 inch (15.9
mm).
3. For grouted masonry, the grout meets one of the following
requirements:
3.1. Grout conforms to ASTM C 476.
3.2. Minimum grout compressive strength equals f ′m
but not less than 2,000 psi (13.79 MPa). The compressive strength of grout shall be determined in
accordance with ASTM C 1019.
v The quality assurance provisions in this section emphasize verification of masonry compressive strengths.
This is accomplished by comparing conservatively estimated strengths (based on unit strength and mortar
type) or tested prism strengths to the specified compressive strength of the masonry, f ′m, and, when required, by mortar, grout or both to see that they are in
compliance.
These quality assurance methods are for general
consistency of the constructed masonry. Masonry is relatively strong in compression and thus rarely fails in that
manner, but rather in flexural tension. Compression
tests are required, however, because they are simple
ways of assessing quality.
As implied in the above paragraph, two methods are
prescribed in Section 2105.2 to judge acceptance relative to the compressive strength of the masonry assemblage—the unit strength method and the prism test
method. These are described in Section 2105.2 and in
this commentary. When the strength of constructed masonry is questioned, testing of prisms that have been
saw cut from the masonry is permitted in accordance
with Section 2105.3.
2105.2.1 Compliance with f ¢m. Compressive strength of masonry shall be considered satisfactory if the compressive
strength of each masonry wythe and grouted collar joint equals
or exceeds the value of f ¢m.
v Design of structural masonry is based on the specified
compressive strength of the masonry, f ′m. This strength
is required to be shown on the contract documents,
since structural design is based on it. Strength of the
constructed masonry determined by the unit strength
method or the prism strength method is required to
equal or exceed the specified compressive strength of
the masonry, f ′m.
In a multiwythe wall designed as a composite wall,
the compressive strength of masonry for each wythe or
grouted collar joint must equal or exceed f ′m.
2105.2.2 Determination of compressive strength. The compressive strength for each wythe shall be determined by the unit
strength method or by the prism test method as specified herein.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
v This section prescribes the conditions under which the
unit strength method can be used for clay masonry.
These conditions include requirements for clay masonry units, maximum mortar joint thickness and grout.
TABLE 2105.2.2.1.1
COMPRESSIVE STRENGTH OF CLAY MASONRY
NET AREA COMPRESSIVE STRENGTH OF CLAY
MASONRY UNITS (psi)
Type M or S mortar
Type N mortar
NET AREA
COMPRESSIVE
STRENGTH OF
MASONRY (psi)
1,700
2,100
1,000
3,350
4,150
1,500
4,950
6,200
2,000
6,600
8,250
2,500
8,250
10,300
3,000
9,900
—
3,500
13,200
—
4,000
For SI: 1 pound per square inch = 0.00689 Mpa.
v Table 2105.2.2.1.1 lists the compressive strength of
masonry in terms of the strength of the clay masonry
unit and the mortar type. This table is based on the research results cited in the commentary to ACI
530.1/ASCE 6/TMS 602. A similar table has been used
successfully in both ACI 530.1/ASCE 6/TMS 602 and
the Uniform Building Code™ (UBC) since 1988.
21-33
2105.2.2.1.2 – 2105.3
MASONRY
The designer can use this table to estimate a specified compressive strength of masonry to use in design,
based on the expected strength of the clay masonry
units and the specified mortar type. The contractor can
use the table to find what clay unit masonry strength and
mortar type are needed to comply with the specified
strength of the masonry, f ′m, given in the contract documents. The column entitled “Net Area Compressive
Strength of Masonry” must equal or exceed the specified strength of the masonry, f ′m.
2105.2.2.1.2 Concrete masonry. The compressive strength of
masonry shall be determined based on the strength of the unit
and type of mortar specified using Table 2105.2.2.1.2, provided:
1. Units conform to ASTM C 55 or ASTM C 90 and are sampled and tested in accordance with ASTM C 140.
2. Thickness of bed joints does not exceed 5/8 inch (15.9
mm).
3. For grouted masonry, the grout meets one of the following
requirements:
3.1. Grout conforms to ASTM C 476.
3.2. Minimum grout compressive strength equals f ¢m
but not less than 2,000 psi (13.79 MPa). The compressive strength of grout shall be determined in
accordance with ASTM C 1019.
v This section prescribes the conditions under which the
unit strength method can be used for concrete masonry.
These conditions include requirements for the concrete
masonry units, maximum mortar joint thickness and
grout. Concrete masonry units must be tested in accordance with ASTM C 140.
TABLE 2105.2.2.1.2
COMPRESSIVE STRENGTH OF CONCRETE MASONRY
NET AREA COMPRESSIVE STRENGTH OF
CONCRETE MASONRY UNITS (psi)
Type M or S mortar
Type N mortar
NET AREA
COMPRESSIVE
STRENGTH OF
MASONRY (psi)a
1,250
1,300
1,000
1,900
2,150
1,500
2,800
3,050
2,000
3,750
4,050
2,500
4,800
5,250
3,000
For SI:
1 inch = 25.4 mm, 1 pound per square inch = 0.00689 MPa.
a. For units less than 4 inches in height, 85 percent of the values listed.
v Table 2105.2.2.1.2 lists the compressive strength of
masonry in terms of the strengths of the concrete masonry units and the mortar type. This table is based on
the research cited in the commentary to ACI
530.1/ASCE 6/TMS 602. A similar table has been used
successfully in both ACI 530.1/ASCE 6/TMS 602 and
the UBC since 1988.
The designer can use this table to estimate a specified compressive strength of masonry for use in design,
based on the expected strength of the concrete ma-
21-34
sonry units and the specified mortar type. The contractor can use the table to find what concrete masonry
strength and mortar type are needed to comply with the
specified strength of the masonry, f ′m, given in the contract documents. The column entitled “Net Area Compressive Strength of Masonry” must equal or exceed the
specified strength of the masonry, f ′m.
2105.2.2.2 Prism test method.
v The prism test method is used when required in the project specifications or when the restrictions of Section
2105.2.2.1 do not apply. Prisms are required to be constructed in accordance with ASTM C 1314 using the
same materials and workmanship as in the structure.
ASTM C 1314 replaced ASTM E 447 for field-constructed prism specimens, which was referenced in editions of the specification prior to 1999. The use of ASTM
C 1314 is intended to address many of the concerns
over the difficulty and imprecision of ASTM E 447 for
large prisms.
2105.2.2.2.1 General. The compressive strength of masonry
shall be determined by the prism test method:
1. Where specified in the construction documents.
2. Where masonry does not meet the requirements for application of the unit strength method in Section 2105.2.2.1.
v Prism tests are required whenever specified and whenever the masonry does not meet the restrictions for the
unit strength method.
2105.2.2.2.2 Number of prisms per test. A prism test shall
consist of three prisms constructed and tested in accordance
with ASTM C 1314.
v Whenever prism testing is specified or used, three
prism specimens must be constructed and tested in accordance with ASTM C 1314.
2105.3 Testing prisms from constructed masonry. When approved by the building official, acceptance of masonry that does
not meet the requirements of Section 2105.2.2.1 or 2105.2.2.2
shall be permitted to be based on tests of prisms cut from the masonry construction in accordance with Sections 2105.3.1,
2105.3.2 and 2105.3.3.
v While uncommon, there are times when the strength of
masonry determined by the unit strength method or
prism test method may be questioned or may be lower
than the specified strength. Because low strengths
could result from inappropriate testing procedures or
unintentional damage to the test specimens, prisms
may be saw cut from the completed masonry wall and
tested. This section prescribes procedures for such
tests.
Such testing is difficult, requires at least 28 days and
requires replacement of the affected wall area. Therefore, every effort should be taken so that strengths de-
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2105.3.1 – 2106.1.1
termined by the unit strength method or the prism test
method are adequate.
2105.3.1 Prism sampling and removal. A set of three masonry
prisms that are at least 28 days old shall be saw cut from the masonry for each 5,000 square feet (465 m2) of the wall area that is
in question but not less than one set of three masonry prisms for
the project. The length, width and height dimensions of the
prisms shall comply with the requirements of ASTM C 1314.
Transporting, preparation and testing of prisms shall be in accordance with ASTM C 1314.
v Removal of prisms from a constructed wall requires
care so that the prism is not damaged and that damage
to the wall is minimal. Prisms must be representative of
the wall, yet not contain reinforcing steel, which would
bias the results. As with a prism test of newly constructed masonry, a prism test from existing masonry
requires three prism specimens.
2105.3.2 Compressive strength calculations. The compressive
strength of prisms shall be the value calculated in accordance
ASTM C 1314, except that the net cross-sectional area of the
prism shall be based on the net mortar bedded area.
structural strength, ductility and stability against the dynamic effects of earthquakes. As seismic demand
increases, the provisions require more positive connection
between structural elements, increased ductility and
greater material reliability.
Chapter 16 contains state-of-the-art criteria for seismic
design, including provisions applicable to masonry. The
requirements of Chapter 16 for seismic resistance (for example, design forces and masonry detailing) remain applicable and are discussed in the commentary to that chapter. Compliance with Chapter 21 is not a substitute for
compliance with the seismic provisions of Chapter 16.
More information on seismic design is contained in the
commentaries to Chapter 16 and the NEHRP Provisions.
To comply with the provisions in Section 2106, the seismic design category must be determined for the building
or structure under consideration. Refer to the commentary
to Chapter 16 for information on determining the seismic
design category and other seismic parameters. Based on
the seismic design category, the designer needs to meet
the minimum requirements of Section 2106.2, 2106.3,
2106.4, 2106.5 or 2106.6 as well as the referenced MSJC
Code sections.
v Compressive strength calculations from saw-cut specimens must be based on the net mortar bedded area,
which must be determined before the prism is tested.
The testing agency must determine this area accurately.
2106.1.1 Basic seismic-force-resisting system. Buildings relying on masonry shear walls as part of the basic seismic-force-resisting system shall comply with Section 1.13.2.2 of ACI
530/ASCE 5/TMS 402 or with Section 2106.1.1.1, 2106.1.1.2
or 2106.1.1.3.
2105.3.3 Compliance. Compliance with the requirement for the
specified compressive strength of masonry, f ¢m, shall be considered satisfied provided the modified compressive strength
equals or exceeds the specified f ¢m. Additional testing of specimens cut from locations in question shall be permitted.
v A basic seismic-force-resisting system must be defined
for all buildings. Most masonry buildings use shear
walls to serve as the basic seismic-force-resisting system, although other systems are sometimes used (such
as concrete or steel frames with masonry infill). Such
shear walls must be designed by the engineered methods in Section 2107 or 2108, unless the structure is assigned to Seismic Design Category A, in which case the
empirical provisions of Section 2109 may be used.
There are three types of masonry shear wall systems
that are recognized by the IBC, but are not specifically
listed in the MSJC Code. They are ordinary plain prestressed shear walls (Section 2106.1.1.1), intermediate
prestressed masonry shear walls (Section 2106.1.1.2)
and special prestressed masonry shear walls (Section
2106.1.1.3). The shear wall systems recognized by the
MSJC Code are discussed below.
Ordinary plain masonry shear walls (see Section
1.13.2.2.1 of ACI 530/ASCE 5/TMS 402) meet minimum requirements only and thus may be used only in
areas of low seismic risk. Plain masonry walls are designed as unreinforced masonry (by the noted section),
although they may in fact contain reinforcement.
Ordinary reinforced masonry shear walls (see Section 1.13.2.2.3 of ACI 530/ASCE 5/TMS 402) are required to meet minimum requirements for reinforced
masonry as noted in the referenced section. Because
they contain reinforcement, their performance is expected to be better than that of plain masonry shear
walls and they are accordingly permitted in areas of
both low and moderate seismic risk. Additionally, these
v Strengths determined from saw-cut prisms must equal
or exceed the specified strength of masonry, f ′m.
SECTION 2106
SEISMIC DESIGN
2106.1 Seismic design requirements for masonry. Masonry
structures and components shall comply with the requirements
in Section 1.13.2.2 of ACI 530/ASCE 5/TMS 402 and Section
1.13.3, 1.13.4, 1.13.5, 1.13.6 or 1.13.7 of ACI 530/ASCE
5/TMS 402 depending on the structure’s seismic design category as determined in Section 1616.3. All masonry walls, unless
isolated on three edges from in-plane motion of the basic structural systems, shall be considered to be part of the seismic-force-resisting system. In addition, the following
requirements shall be met.
v Section 2106 contains minimum requirements for masonry structures based upon their seismic design category. This section requires the use of MSJC Code seismic
design criteria. Requirements established for various seismic risk categories are cumulative from lower to higher
categories. These prescriptive and design-oriented provisions have been established to improve the performance
of masonry during seismic events by providing additional
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-35
2106.1.1.1 – 2106.1.1.3.2
walls have more favorable seismic design parameters,
including higher response modification factors, R, than
plain masonry shear walls. When assigned to moderate
seismic risk areas (Seismic Design Category C), however, minimum reinforcement is required as noted in
Section 2106.4.
Detailed plain masonry shear walls (see Section
1.13.2.2.2 of ACI 530/ASCE 5/TMS 402) are designed
as unreinforced masonry in accordance with the section
noted, but contain minimum reinforcement in the horizontal and vertical directions. Because of this reinforcement, these walls have more favorable seismic design
parameters, including higher response modification factors, R, than ordinary plain masonry shear walls.
Intermediate reinforced masonry shear walls (see
Section 1.13.2.2.4 of ACI 530/ASCE 5/TMS 402) are
designed as reinforced masonry as noted in the referenced section and are also required to contain a minimum amount of prescriptive reinforcement. Because
they contain reinforcement, their seismic performance
is better than that of plain masonry shear walls and they
are accordingly permitted in both areas of low and moderate seismic risk. Additionally, these walls have more
favorable seismic design parameters, including higher
response modification factors, R, than plain masonry
shear walls and ordinary reinforced masonry shear
walls.
Special reinforced masonry shear walls (see Section
1.13.2.2.5 of ACI 530/ASCE 5/TMS 402) are designed
as reinforced masonry as noted in the referenced section and are also required to meet restrictive reinforcement and material requirements. Because of these reinforcement and material requirements, they are
permitted to be used in all seismic risk areas. Additionally, these walls have the most favorable seismic design parameters, including the highest response modification factors, R, of any of the masonry shear wall
types.
2106.1.1.1 Ordinary plain prestressed masonry shear walls.
Ordinary plain prestressed masonry shear walls shall comply
with the requirements of Chapter 4 of ACI 530/ASCE 5/TMS
402.
v This type of shear wall is recognized as a basic seismic-force-resisting system under the code and it must
comply with the limitations for these systems in Section
1617.6. The only other stipulation is that it comply with
the prestressed masonry requirements of the MSJC
Code.
2106.1.1.2 Intermediate prestressed masonry shear walls.
Intermediate prestressed masonry shear walls shall comply with
the requirements of Section 1.13.2.2.4 of ACI 530/ASCE
5/TMS 402 and shall be designed by Chapter 4, Section 4.5.3.3,
of ACI 530/ASCE 5/TMS 402 for flexural strength and by Section 3.2.4.1.2 of ACI 530/ASCE 5/TMS 402 for shear strength.
Sections 1.13.2.2.5(a), 3.2.3.5 and 3.2.4.3.2(c) of ACI
530/ASCE 5/TMS 402 shall be applicable for reinforcement.
Flexural elements subjected to load reversals shall be symmetri21-36
MASONRY
cally reinforced. The nominal moment strength at any section
along a member shall not be less than one-fourth the maximum
moment strength. The cross-sectional area of bonded tendons
shall be considered to contribute to the minimum reinforcement
in Section 1.13.2.2.4 of ACI 530/ASCE 5/TMS 402. Tendons
shall be located in cells that are grouted the full height of the
wall.
v This type of shear wall is recognized as a basic seismic-force-resisting system under the code and it must
comply with the limitations for these systems in Section
1617.6. Besides requiring that it comply with the prestressed masonry provisions of the MSJC Code, additional requirements must be met that are consistent with
the results of research and testing carried out in New
Zealand. These additional requirements intend that the
walls develop their flexural capacity prior to shear failure. Tendons are limited to cells that are fully grouted,
since testing has not substantiated that laterally unrestrained tendons are satisfactory for moderate seismic
hazards.
2106.1.1.3 Special prestressed masonry shear walls. Special
prestressed masonry shear walls shall comply with the requirements of Section 1.13.2.2.5 of ACI 530/ASCE 5/TMS 402 and
shall be designed by Chapter 4, Section 4.5.3.3, of ACI
530/ASCE 5/TMS 402 for flexural strength and by Section
3.2.4.1.2 of ACI 530/ASCE 5/TMS 402 for shear strength. Sections 1.13.2.2.5(a), 3.2.3.5 and 3.2.4.3.2(c) of ACI 530/ASCE
5/TMS 402 shall be applicable for reinforcement. Flexural elements subjected to load reversals shall be symmetrically reinforced. The nominal moment strength at any section along a
member shall not be less than one-fourth the maximum moment
strength. The cross-sectional area of bonded tendons shall be
considered to contribute to the minimum reinforcement in Section 1.13.2.2.5 of ACI 530/ASCE 5/TMS 402. Special prestressed masonry shear walls shall also comply with the
requirements of Section 3.2.3.5 of ACI 530/ASCE 5/TMS 402.
v This type of shear wall is recognized as a basic seismic-force-resisting system under the code and it must
comply with the limitations for these systems in Section
1617.6. Besides requiring that it comply with the prestressed masonry provisions of the MSJC Code, additional limitations apply that are based on the testing
used to substantiate these systems. These additional
requirements intend that the walls develop their flexural
capacity prior to shear failure.
2106.1.1.3.1 Prestressing tendons. Prestressing tendons shall
consist of bars conforming to ASTM A 722.
v Test specimens for prestressed masonry shear wall
systems used only high-strength bar tendons, indicating
that is an appropriate restriction for these systems that
are intended for exposure to high seismic hazards.
2106.1.1.3.2 Grouting. All cells of the masonry wall shall be
grouted.
v Testing of prestressed masonry shear wall systems indicates that exposure to high seismic hazard is only per2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2106.2 – 2106.5.2
missible if all cells of the hollow concrete masonry unit
(CMU) wall are grouted solid. This is because partially
grouted walls have demonstrated somewhat brittle
behavior.
ductility and load-transfer capability in masonry structures assigned to SDC C. The minimum provisions for
improved performance of masonry construction in SDC
C must be met, regardless of the method of design.
2106.2 Anchorage of masonry walls. Masonry walls shall be
anchored to the roof and floors that provide lateral support for
the wall in accordance with Section 1604.8.2.
2106.4.1 Design of discontinuous members that are part of
the lateral-force-resisting system. Columns and pilasters that
are part of the lateral-force-resisting system and that support reactions from discontinuous stiff members such as walls shall be
provided with transverse reinforcement spaced at no more than
one-fourth of the least nominal dimension of the column or pilaster. The minimum transverse reinforcement ratio shall be
0.0015. Beams supporting reactions from discontinuous walls
or frames shall be provided with transverse reinforcement
spaced at no more than one-half of the nominal depth of the
beam. The minimum transverse reinforcement ratio shall be
0.0015.
v This provision applies to all masonry structures, regardless of seismic design category. Because masonry
walls typically depend on lateral support from floors and
roofs, they are required to be anchored directly to those
elements. Section 1604.8.2 prohibits reliance on friction
(from dead load) alone to hold walls, floors and roofs together and prescribes minimum forces for design of
anchorage.
2106.3 Seismic Design Category B. Structures assigned to
Seismic Design Category B shall conform to the requirements
of Section 1.13.4 of ACI 530/ASCE 5/TMS 402 and to the additional requirements of this section.
v Requirements in Seismic Design Category (SDC) B are
slightly more restrictive than in SDC A. Since the requirements are cumulative with each successive SDC,
masonry assigned to SDC B must meet the requirements for SDC A (Section 1.13.3 of the MSJC Code) as
well as Section 1.13.4 of the MSJC Code and the requirements in Section 2106.3. Therefore, besides those
requirements in Section 2106.2, masonry shear walls
must also be one of the types discussed in the commentary to Section 2106.1.1 and be rationally designed in
this SDC and above.
2106.3.1 Masonry walls not part of the lateral-force-resisting system. Masonry partition walls, masonry screen walls and
other masonry elements that are not designed to resist vertical or
lateral loads, other than those induced by their own mass, shall
be isolated from the structure so that the vertical and lateral
forces are not imparted to these elements. Isolation joints and
connectors between these elements and the structure shall be designed to accommodate the design story drift.
v So that seismic loads are not inadvertently transferred
into elements such as masonry partition and screen
walls, they are required to be isolated from the seismic-force-resisting system. However, these elements
need out-of-plane support. Appropriate connectors are
available and should be used. This is, in effect, a modification to the seismic requirements of the MSJC Code,
since in that standard this is a requirement for SDC C
structures and higher.
2106.4 Additional requirements for structures in Seismic
Design Category C. Structures assigned to Seismic Design
Category C shall conform to the requirements of Section 1.13.5
of ACI 530/ASCE 5/TMS 402 and the additional requirements
of this section.
v In addition to the requirements of SDC, minimum levels
of reinforcement and detailing are required to enhance
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
v The requirements in this section are intended to reduce
the chance of local failure or collapse in elements supporting discontinuous portions of the lateral-force-resisting system by increasing the strength and toughness of those elements. Elements used to redistribute
or transfer the effects of seismic overturning are susceptible to local inelastic response that can significantly
impair the ability of the lateral-force-resisting system to
achieve the required overall ductility. The provisions in
this section are intended to increase the ability of elements to resist inelastic deformations. This allows inelastic deformations to be distributed throughout the
buildings, as is implied by the large response modification factors used in design.
2106.5 Additional requirements for structures in Seismic
Design Category D. Structures assigned to Seismic Design Category D shall conform to the requirements of Section 2106.4,
Section 1.13.6 of ACI 530/ASCE 5/TMS 402 and the additional
requirements of this section.
v Requirements in this section parallel most of the requirements in the MSJC Code.
2106.5.1 Loads for shear walls designed by the working
stress design method. When calculating in-plane shear or diagonal tension stresses by the working stress design method, shear
walls that resist seismic forces shall be designed to resist 1.5
times the seismic forces required by Chapter 16. The 1.5 multiplier need not be applied to the overturning moment.
v This provision is based on a similar provision from the
UBC. It requires that the in-plane shear stresses due to
seismic loading be increased by 50 percent for design
purposes and is intended to provide adequate strength
and ductility in shear walls of structures in seismically
active areas.
2106.5.2 Shear wall shear strength. For a shear wall whose
nominal shear strength exceeds the shear corresponding to development of its nominal flexural strength, two shear regions exist.
For all cross sections within a region defined by the base of
21-37
2106.6 – 2107.2.2
MASONRY
the shear wall and a plane at a distance Lw above the base of the
shear wall, the nominal shear strength shall be determined by
Equation 21-1.
load combinations, however, pseudo-strength design is
not needed and is therefore not permitted.
2107.2 Modifications to ACI 530/ASCE 5/TMS 402.
Vn = An ρn fy
(Equation 21-1)
The required shear strength for this region shall be calculated
at a distance Lw /2 above the base of the shear wall, but not to exceed one-half story height.
For the other region, the nominal shear strength of the shear
wall shall be determined from Section 2108.
v The intent of this provision is to provide a ductile flexural
limit state. The plastic hinge region is considered to extend vertically from the base of the wall to a distance
equal to the plan length of the wall. In this region, the
shear strength of the wall is based on the transverse reinforcement only. Above the plastic hinge, the shear
strength of the wall is based on both the masonry and
the transverse reinforcement.
2106.6 Additional requirements for structures in Seismic
Design Category E or F. Structures assigned to Seismic Design
Category E or F shall conform to the requirements of Section
2106.5 and Section 1.13.7 of ACI 530/ASCE 5/TMS 402.
v Additional restrictions are imposed on buildings assigned to the highest seismic risk categories.
SECTION 2107
WORKING STRESS DESIGN
2107.1 General. The design of masonry structures using working stress design shall comply with Section 2106 and the requirements of Chapters 1 and 2, except Section 2.1.2.1 and
2.1.3.3 of ACI 530/ASCE 5/TMS 402. The text of ACI
530/ASCE 5/TMS 402 shall be modified as follows.
v Section 2107 adopts the working stress design method
of Chapters 1 and 2 of the MSJC Code (ACI 530/ASCE
5/TMS 402) with modifications that the IBC Structural
Committee felt were needed. This method of engineered masonry design has been used successfully for
years and remains the dominant method of designing
masonry structures.
Refer to the commentary to Chapters 1 and 2 of the
MSJC Code for additional information on the working
stress design method for masonry. This section also requires conformance to the seismic design provisions of
Section 2106. The sections of the MSJC Code specifically not adopted exclude redundant or conflicting provisions such as the MSJC load combinations, which are
only intended to apply where no such load combinations
are included in the building code.
The pseudo-strength design provision of ACI
530/ASCE 5/TMS 402, Section 2.1.3.3, is also excluded. This method allows masonry to be designed using strength-based seismic loads and working stress
provisions. Since Chapter 16 contains service-level
21-38
v The IBC Structural Subcommittee considered and
adopted several modifications to the MSJC Code regarding special inspection, column requirements, splice
requirements for reinforcement (both lap splices and
mechanical or welded splices) and maximum bar size.
These modifications supersede the MSJC Code provisions when working stress design is used.
2107.2.1 ACI 530/ASCE 5/TMS 402, Chapter 2. Special inspection during construction shall be provided as set forth in
Section 1704.5.
v The inspection provisions for masonry in Chapter 17
were based on the inspection requirements in the MSJC
Code and Specification, with several key modifications.
Masonry designed by working stress procedures must
be inspected in accordance with the IBC inspection
requirements.
2107.2.2 ACI 530/ASCE 5/TMS 402, Section 2.1.6. Masonry
columns used only to support light-frame roofs of carports,
porches, sheds or similar structures with a maximum area of 450
square feet (41.8 m2) assigned to Seismic Design Category A, B
or C are permitted to be designed and constructed as follows:
1. Concrete masonry materials shall be in accordance with
Section 2103.1. Clay or shale masonry units shall be in accordance with Section 2103.2.
2. The nominal cross-sectional dimension of columns shall
not be less than 8 inches (203 mm).
3. Columns shall be reinforced with not less than one No. 4
bar centered in each cell of the column.
4. Columns shall be grouted solid.
5. Columns shall not exceed 12 feet (3658 mm) in height.
6. Roofs shall be anchored to the columns. Such anchorage
shall be capable of resisting the design loads specified in
Chapter 16.
7. Where such columns are required to resist uplift loads, the
columns shall be anchored to their footings with two No. 4
bars extending a minimum of 24 inches (610 mm) into the
columns and bent horizontally a minimum of 15 inches
(381 mm) in opposite directions into the footings. One of
these bars is permitted to be the reinforcing bar specified
in Item 3 above. The total weight of a column and its footing shall not be less than 1.5 times the design uplift load.
v Section 2107.2.2 exempts lightly loaded columns (such
as those that support carport roofs, which experience
primarily axial tension and flexure in high-wind events)
from the prescriptive requirements of Section 2.1.6 of
the MSJC Code. All other columns need to comply with
Section 2.1.6 of the MSJC Code. This provision is similar to one in the Standard Building Code© (SBC©)and is
intended to relax an aspect of the MSJC Code, which
defines columns by geometry rather than function. According to that document, masonry members of a cer2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2107.2.3 – 2108.1
tain geometry, even though they act primarily in flexure,
are classified as columns and thus must meet minimum
reinforcement requirements for columns.
2107.2.3 ACI 530/ASCE 5/TMS 402, Section 2.1.10.6.1.1, lap
splices. The minimum length of lap splices for reinforcing bars
in tension or compression, lld, shall be calculated by Equation
21-2, but shall not be less than 15 inches (380 mm).
l ld =
016
. d b2 f y γ
(Equation 21-2)
thickness and shall not exceed one-quarter of the least dimension of the cell, course or collar joint in which it is placed.
v Allowing large bars in the masonry walls can result in an
overreinforced section that increases the risk of a brittle
failure. This section specifies limits on the diameter of reinforcement that are not in the MSJC Code in order to prevent potential problems with overreinforcement and congestion of reinforcement. The requirements are based on
tests of splices and successful performance in construction.
K f 'm
For SI: l ld =
1.95d b2 f y γ
K f 'm
where:
db = Diameter of reinforcement, inches (mm).
fy = Specified yield stress of the reinforcement or the anchor bolt, psi (MPa).
f ′m = Specified compressive strength of masonry at age of
28 days, psi (MPa).
lld = Minimum lap splice length, inches (mm).
K = The lesser of the masonry cover, clear spacing between
adjacent reinforcement or five times db, inches (mm).
γ
= 1.0 for No. 3 through No. 5 reinforcing bars. 1.4 for
No. 6 and No. 7 reinforcing bars. 1.5 for No. 8 through
No. 9 reinforcing bars.
v This modification brings consistency to the requirements for splice lengths for reinforcement according to
working stress and strength design. The IBC Structural
Committee accepted this modification based on broad
support from the masonry industry and engineers, since
it was noted that existing splice-length requirements are
overly conservative for small bar sizes and
unconservative for large ones. Note that Section
2107.2.5 prohibits lap spicing of bars that are larger
than No. 9.
Traditional requirements for development lengths
and splices of reinforcing bars in masonry have long
been questioned because of the disparity between required development lengths (and lap lengths) typically
used for masonry and those used in reinforced concrete. This provision is based on requirements that have
been in the UBC for several years, but also incorporates
updates based on extensive research that supports the
position that development lengths and lap splice
lengths traditionally used were often overly conservative for small bars and unconservative for large ones.
Equation 21-2 is based on that research and indicates
that the required lap length and development length depend on bar diameter, the cover depth of masonry over
the reinforcing steel, the strength of the masonry and
the strength of the reinforcing steel.
2107.2.4 ACI 530/ASCE 5/TMS 402, maximum bar size. The
bar diameter shall not exceed one-eighth of the nominal wall
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2107.2.5 ACI 530/ASCE 5/TMS 402, splices for large bars.
Reinforcing bars larger than No. 9 in size shall be spliced using
mechanical connectors in accordance with ACI 530/ASCE
5/TMS 402, Section 2.1.10.6.3.
v Research has showed that effectively lap splicing large reinforcing bars in masonry is difficult and impractical because of the excessive lap lengths required. This section
adds a provision not in the MSJC Code requiring mechanical splices for all bars larger than No. 9 (32 mm) in diameter. Such large bars are rarely required in masonry and do
not perform as well as a larger number of smaller bars.
2107.2.6 ACI 530/ASCE 5/TMS 402, Maximum reinforcement percentage. Special reinforced masonry shear walls having a shear span ratio, M/Vd, equal to or greater than 1.0 and
having an axial load, P greater than 0.05 f ′mAn which are subjected to in-plane forces, shall have a maximum reinforcement
ratio, rmax, not greater than that computed as follows:
rmax =
nf m′
fy 

2 fy  n +

f m′ 

(Equation 21-3)
v The allowable stress design (ASD) provisions of the
MSJC Code have no limit on the maximum reinforcement ratio. This section places such a limit on the maximum reinforcement ratio in special reinforced masonry
shear walls. It is necessary to account for the relatively
high potential for inelastic response in such systems.
This requirement is based on the recommendations
of a blue-ribbon panel appointed by the Masonry Alliance for Codes and Standards (MACS). It was the
panels’ conclusion that these requirements should only
apply to the design of shear walls for in-plane forces that
have significant axial load (P >.05 f ′m An) and that are
controlled by flexure (i.e., M/Vd $ 1.0).
SECTION 2108
STRENGTH DESIGN OF MASONRY
2108.1 General. The design of masonry structures using
strength design shall comply with Section 2106 and the requirements of Chapters 1 and 3 of ACI 530/ASCE 5/TMS 402.
The minimum nominal thickness for hollow clay masonry
21-39
2108.2 – 2108.3
in accordance with Section 3.2.5.5 of ACI 530/ASCE 5/TMS
402 shall be 4 inches (102 mm).
v The first edition of the IBC contained extensive strength
design requirements, since a consensus standard for the
strength design of masonry did not yet exist. Since
strength design procedures were incorporated in the 2002
edition of the MSJC Code (ACI 530/ASCE 5/TMS 402),
this section now requires that strength design be in accordance with Chapters 1 and 3 of the MSJC Code with some
modifications to specific sections. For instance, the minimum nominal thickness of 6 inches (152 mm) for hollow
day units is reduced to 4 inches (102 mm). This section
also invokes the minimum seismic requirements of Section 2106 for all masonry designed by this method. Additionally, masonry designed by this method must be inspected during construction in accordance with the
special inspection provisions of Section 1704.5.
2108.2 ACI 530/ASCE 5/TMS 402, Section 3.2.2(g). Modify
Section 3.2.2(g) as follows:
3.2.2(g). The relationship between masonry compressive stress
and masonry strain shall be assumed to be defined by the following:
Masonry stress of 0.80 ƒ′m shall be assumed uniformly distributed over an equivalent compression zone bounded by edges
of the cross section and a straight line located parallel to the neutral axis at a distance, a = 0.80 c, from the fiber of maximum
compressive strain. The distance, c, from the fiber of maximum
strain to the neutral axis shall be measured perpendicular to that
axis. For out-of-plane bending, the width of the equivalent stress
block shall not be taken greater than six times the nominal thickness of the masonry wall or the spacing between reinforcement,
whichever is less. For in-plane bending of flanged walls, the effective flange width shall not exceed six times the thickness of
the flange.
v This section modifies the design assumptions of the
MSJC Code. These principles have traditionally been
used for reinforced masonry members designed by the
strength method. The values for the maximum usable
strain are based on extensive research of masonry materials and are different from the values used in the 1997
UBC. Concerns have been raised regarding the implied
precision of the values. However, the reported values
for the maximum usable strain accurately represent
those observed during testing.
While tension may still develop in the masonry of a reinforced element, it is not considered effective in resisting design loads. However, the tensile resistance of masonry is considered implicitly in computing the stiffness
of reinforced masonry. If it were not, the effective moment of inertia would always be just the cracked transformed moment of inertia.
The modification made by the IBC provides direction
on the stress block width for out-of-plane bending as
well as for flanged walls. These limitations are consistent with the NEHRP Provisions and are based on usual
practice under previous codes.
21-40
MASONRY
2108.3 ACI 530/ASCE 5/TMS 402, Section 3.2.3.4. Modify
Section 3.2.3.4 (b) and (c) as follows:
3.2.3.4 (b). A welded splice shall have the bars butted and
welded to develop at least 125 percent of the yield strength, ƒy,
of the bar in tension or compression, as required. Welded splices
shall be of ASTM A 706 steel reinforcement. Welded splices
shall not be permitted in plastic hinge zones of intermediate or
special reinforced walls or special moment frames of masonry.
3.2.3.4 (c). Mechanical splices shall be classified as Type 1 or
2 according to Section 21.2.6.1 of ACI 318. Type 1 mechanical
splices shall not be used within a plastic hinge zone or within a
beam-column joint of intermediate or special reinforced masonry shear walls or special moment frames. Type 2 mechanical
splices are permitted in any location within a member.
v This section modifies the strength design splice requirements for consistency with the 2000 edition of the NEHRP
Provisions. Splices for reinforcement can be achieved by
lapping the reinforcement, welding the reinforcement or
mechanical splicing.
Two modifications are made to welded splice requirements [Item (b)]. Splices in reinforcing steel used in the lateral-force-resisting system subjected to high seismic
strains must be able to develop the strength of the steel in
order to achieve the required performance. To be successfully welded, the chemistry of the steel must be controlled to limit carbon content as well as other elements,
such as sulfur and phosphorus. Since the chemistry of reinforcing steel conforming to ASTM A 615, for example, is
not controlled and is likely to be unknown, a weld that develops the strength of the steel is not guaranteed. ASTM A
706 steel, on the other hand, has controlled chemistry and
can be reliably welded; therefore, if splices are to be accomplished by welding, the use of ASTM A 706 reinforcing steel is mandatory.
Welded splices are required to be able to develop at
least 125 percent of the yield strength of the spliced
rebars; however, reinforcing steel conforming to ASTM A
706 or for that matter ASTM A 615 or A 996 can have an
actual yield strength greater than 125 percent of the minimum required yield strength. This means a code-conforming welded splice may conceivably fail before the spliced
bars have yielded, thereby limiting the inelastic
deformability of that structural member. The use of welded
splices is, therefore, prohibited at locations of potential
plastic hinging of members in structural systems that are
expected to undergo significant inelastic response in resisting forces due to earthquakes.
The modification to mechanical splices in Item (c) requires that the splice be classified in accordance with ACI
318 as Class 1 or Class 2. This is due to the fact that reinforcing steel is predominantly produced from remelted
steel scrap, making it difficult to control the strength. The
resulting products tend to have a strength considerably
higher than the specified yield strength. This is similar to
the situation that has occurred in structural steel where the
actual yield strength can be much greater than the specified yield strength. Since there is no upper limit on the yield
strength (except for ASTM A 706) and only a minimum required yield strength, most reinforcing steel will have a
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2108.4 – 2109.1.1
higher yield point than that specified.
Testing by the California Department of Transportation
(CALTRANS) indicates the overstrength can be as much
as 60 percent over the specified strength. Cyclic tests of
splices meeting only the 125-percent criterion (i.e. Class
1) show that, in many cases, they cannot survive several
excursions in the post yield range as imposed by cyclic
testing. Splices in reinforcing steel used in the lateral-force-resisting system in plastic hinge zones and
beam-column joints are subjected to high seismic strains,
and they must be able to develop the strength of the steel
in order to achieve the required performance. Hence, the
requirement for a Type 2 splice that develops the specified
tensile strength of the bar.
premises: gravity loads are reasonably centered on
bearing walls; effects of reinforcement are neglected;
walls are laid in running bond and buildings have limited
height, seismic risk and wind loading. The requirements
of and limitations regarding the use of empirical design
reflect these assumptions.
2109.1.1 Limitations. Empirical masonry design shall not be
utilized for any of the following conditions:
1. The design or construction of masonry in buildings assigned to Seismic Design Category D, E or F as specified
in Section 1616, and the design of the seismic-force-resisting system for buildings assigned to Seismic Design
Category B or C.
2108.4 ACI 530/ASCE 5/TMS 402, Section 3.2.3.5.1. Add the
following text to Section 3.2.3.5.1:
2. The design or construction of masonry structures located
in areas where the basic wind speed exceeds 110 mph
(177 km/hr).
For special prestressed masonry shear walls, strain in all
prestressing steel shall be computed to be compatible with a
strain in the extreme tension reinforcement equal to five times
the strain associated with the reinforcement yield stress, fy. The
calculation of the maximum reinforcement shall consider forces
in the prestressing steel that correspond to these calculated
strains.
3. Buildings more than 35 feet (10 668 mm) in height which
have masonry wall lateral-force-resisting systems.
v This MSJC Code section limits the percentages of flexural reinforcement in order to provide ductile behavior.
Overreinforced flexural members can fail in a brittle
mode by the crushing of the masonry. Such failures are
sudden and catastrophic and, therefore, must be
avoided.
Section 2106.1.1.3, covering special prestressed masonry shear walls, requires compliance with this code
section, which includes a modification of the MSJC
Code section specifically for those shear wall types.
This modification clarifies how the reinforcing limitation
is to be met for this structural system.
SECTION 2109
EMPIRICAL DESIGN OF MASONRY
2109.1 General. Empirically designed masonry shall conform
to this chapter or Chapter 5 of ACI 530/ASCE 5/TMS 402.
v This section permits empirical design of masonry by either
the provisions of Section 2109 or Chapter 5 of ACI
530/ASCE 5/TMS 402. This is because nearly all of the requirements in Section 2109 are based on the requirements in Chapter 5 of ACI 530/ASCE 5/TMS 402 with minor modifications. Additional information on these
provisions can be found in the commentary to ACI
530/ASCE 5/TMS 402.
Empirical provisions are design rules developed by experience rather than engineering analysis. The empirical
rules in these provisions are based on records dating back
as far as 1889 in A Treatise on Masonry Construction, by
Ira Baker. The most recent publication providing the basis for these empirical provisions is ANSI A41.1.
This empirical design method is based on several
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
In buildings that exceed one or more of the above limitations, masonry shall be designed in accordance with the engineered design provisions of Section 2107 or 2108, or the
foundation wall provisions of Section 1805.5.
v Empirical design is permitted for structures having limited
seismic risk, wind loading and height. These limitations
are justified, since buildings that were representative of
the historically based empirical provisions are uncommon
today. For example, buildings of the past were smaller,
had more interior masonry walls and typically had different
floor construction than modern buildings.
Where any one of the three stated limitations exists,
the masonry structure is not permitted to be empirically
designed. Engineered design in accordance with Section 2107 or 2108 is required in such instances. Foundation walls complying with Section 1805.5 are also
acceptable.
1. The empirical provisions of Section 2109 and the required referenced standards, plus the seismic loading and detailing requirements of Chapter 16, are
adequate for the level of risk associated with the
seismic-force-resisting systems of buildings located
in Seismic Design Category A. Where masonry is
used for purposes other than the seismic-force-resisting system, the empirical design method may be
used for buildings assigned to Seismic Design Category A, B or C. Engineered design is required for
buildings in higher seismic design categories.
2. This requirement applies individually to the lateral-load-resisting system and to building elements not effectively participating in the lateral-load-resisting
system.
For
example,
empirical design of the lateral-load-resisting system is permitted only where the basic wind speed
does not exceed 110 mph (145 km/hr). Otherwise,
engineered design is required. These are similar
to, but not the same as, the wind load restrictions
21-41
2109.2 – TABLE 2109.2.1.3
in Chapter 5 of the MSJC Code (ACI 530/ASCE
5/TMS 402).
mitted minimum nominal thickness of 6 inches (152
mm), as listed in the exception to this section.
3. The limitation is justified since today’s buildings
are taller than those on which these empirical provisions are based. Empirical design is permitted
for elements not effectively participating in the lateral-load-resisting system. Engineered design is
required where the lateral-load-resisting system
of a building has substantial height.
2109.2.1.2 Cumulative length of shear walls. In each direction in which shear walls are required for lateral stability, shear
walls shall be positioned in two separate planes. The minimum
cumulative length of shear walls provided shall be 0.4 times
the long dimension of the building. Cumulative length of shear
walls shall not include openings or any element whose length
is less than one-half its height.
2109.2 Lateral stability.
v The lateral stability requirements of Section 2109.2 are required for buildings using empirical design for lateral load
resistance. The requirements of this section do not apply
when the engineered masonry design method of Section
2101.1.1 is used. This section contains requirements for
empirical design of lateral-load-resisting systems composed of diaphragms and shear walls.
Requirements include minimum lengths of masonry
shear walls in both principal plan directions of the building
and maximum span-to-width (depth) ratios of floor and
roof diaphragms. Requirements for roofs and dry-stacked,
surface-bonded walls are also part of this section.
Lateral load resistance is a basic requirement for structural design. The distribution of loads within the lateral-load-resisting system is a function of the relative rigidities of diaphragms and shear walls. The
lateral-load-resisting system transfers lateral wind and
seismic forces to the foundation in the form of base shear
and overturning moment and maintains stability of the
structure under gravity loads.
2109.2.1 Shear walls. Where the structure depends upon masonry walls for lateral stability, shear walls shall be provided
parallel to the direction of the lateral forces resisted.
v The shear wall requirements in this section apply where
empirically designed masonry is used for lateral load resistance. Shear walls are required in both principal plan
directions of the structure, parallel to the lateral loads
required in Chapter 16. Load-bearing walls serve as
shear walls.
2109.2.1.1 Shear wall thickness. Minimum nominal thickness of masonry shear walls shall be 8 inches (203 mm).
Exception: Shear walls of one-story buildings are permitted to be a minimum nominal thickness of 6 inches (152
mm).
v An empirical minimum nominal shear wall thickness of 8
inches (203 mm) is required to transfer lateral loads to
the foundation. This minimum is based on experience.
Shear walls that are also load-bearing walls are required
to comply with the compressive stress requirements of
Section 2106 and the lateral support requirements of Section 2107. Those requirements may govern.
The exception addresses single-story buildings that
have limited lateral loads and, therefore, limited base
shears and overturning moments. This justifies the per21-42
MASONRY
v Figure 2109.2.1.2 diagrams the lengths in each direction of the building, parallel to the lateral loads. The term
“cumulative” refers to the sum of the lengths of shear
wall segments in a single direction. The required length
of shear wall in each direction is 0.4 times the long dimension of the building.
Walls above and below openings such as windows
and doors are not considered to be shear wall segments. Neither are portions of a wall that have a height
of two or more times its length.
2109.2.1.3 Maximum diaphragm ratio. Masonry shear walls
shall be spaced so that the length-to-width ratio of each diaphragm transferring lateral forces to the shear walls does not
exceed the values given in Table 2109.2.1.3.
v For empirical design, this section limits length- (or span)to-width ratios of floor and roof diaphragms between shear
walls, based on the inherent rigidity of the diaphragm construction. This effectively distributes shear walls throughout the structure at adequate intervals for the diaphragm
span.
The assumed deflected shape of a diaphragm is illustrated in Figure 2109.2.1.3(1). Flexible diaphragms deflect
more than rigid ones, possibly resulting in detachment of
components. A rigid diaphragm deflects little and transfers
loads to shear walls in proportion to their relative rigidities
(an important engineered masonry consideration). Symmetrical distribution of shear walls in the building plan is
desirable, reducing torsional rotation of the building under
lateral loads.
TABLE 2109.2.1.3
DIAPHRAGM LENGTH-TO-WIDTH RATIOS
FLOOR OR ROOF DIAPHRAGM
CONSTRUCTION
MAXIMUM LENGTH-TO-WIDTH
RATIO OF DIAPHRAGM PANEL
Cast-in-place concrete
5:1
Precast concrete
4:1
Metal deck with concrete fill
3:1
Metal deck with no fill
2:1
Wood
2:1
v Table 2109.2.1.3 sets the maximum span-to-width ratio
of diaphragms constructed of the listed materials. See
Figure 2109.2.1.3(2) for an illustration of the terms “diaphragm span” (length) and “width” (depth). Concrete diaphragms are permitted to have high span- (length-)
to-width ratios because of their rigidity, whereas wood diaphragms are required to have low span- (length-)
to-width ratios because of their flexibility.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
FIGURE 2109.2.1.2 – FIGURE 2109.2.1.3(1)
5’-8”
6’-0”
4’-0”
4’-0”
4’-0”
4’-0”
6’-0”
5’-8”
10’-0”
6’-0”
24’-0”
10’-0”
12’-8”
Y
X
60’-8”
MINIMUM CUMULATIVE SHEAR WALL LENGTH = 0.4 x LONG DIMENSION
MINIMUM L = 0.4(60.7’) = 24.3’
X - DIRECTION: L = 2(5.7 + 6.0 + 4.0 + 4.0 + 4.0 + 4.0 + 6.0 + 5.7) = 78.8 ft. > 24.3 ft. OK
Y - DIRECTION: L = 2(24.0 + 10.0 + 10.0 + 12.7 + 6.0) = 125.4 ft. > 24.3 ft. OK
For SI:
1 foot = 304.8 mm.
Figure 2109.2.1.2
CUMULATIVE LENGTH OF SHEAR WALL REQUIREMENTS FOR EMPIRICALLY DESIGNED MASONRY
VERTICAL RESISTING ELEMENT
WIDTH (DEPTH)
LATERAL FORCES
DIAPHRAGM
DEFLECTION
DEFLECTED SHAPE
SPAN
Figure 2109.2.1.3(1)
DIAPHRAGM ACTION (PLAN VIEW)
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-43
2109.2.2 – 2109.2.3.2
MASONRY
2109.2.2 Roofs. The roof construction shall be designed so as
not to impart out-of-plane lateral thrust to the walls under roof
gravity load.
v In surface-bonded masonry construction, strength is
lower than conventional masonry construction because
of the lack of solid contact between the units.
Where stresses are not specified in Table 2109.2.3.1,
engineered design in accordance with Section 2107 or
2108 is required.
ROOF DIAPHRAGM
WI
DT
H(
DE
PT
H
)
AN
SP
support all superimposed loads without exceeding the allowable stresses listed in Table 2109.2.3.1. Allowable stresses not
specified in Table 2109.2.3.1 shall comply with the requirements of ACI 530/ASCE 5/TMS 402.
TABLE 2109.2.3.1
ALLOWABLE STRESS GROSS CROSS-SECTIONAL
AREA FOR DRY-STACKED, SURFACE-BONDED
CONCRETE MASONRY WALLS
FLOOR DIAPHRAGM
S
CE
OR
LF
RA
TE
LA
MASONRY SHEAR WALL
DESCRIPTION
S
CE
OR
LF
RA
TE
LA
SPAN
< TABLE 2109.2.1.3 VALUE
WIDTH
Figure 2109.2.1.3(2)
EMPIRICAL MAXIMUM DIAPHRAGM RATIO
MAXIMUM ALLOWABLE STRESS
(psi)
Compression standard block
45
Shear
10
Flexural tension
Vertical span
Horizontal span
18
30
For SI: 1 pound per square inch = 0.006895 Mpa.
v Roofs are not permitted to rely on masonry walls to resist thrust perpendicular to the wall. The low tensile capacity of masonry and the lack of engineered design for
these loads in the empirical provisions result in this requirement. Connections that apply thrust perpendicular
to the wall are not permitted.
As another example, a wood frame cathedral ceiling
does not, by design, have ceiling joists to resist outward
thrust. If the ridge beam is not designed for vertical support and limited deflection, opposing sloped rafters usually transfer thrust to the outside walls.
Consideration of horizontal thrust is also necessary for
truss connections, especially scissor trusses. In a truss,
the bottom chord is usually in tension. Chord elongation
can impart significant lateral thrust perpendicular to masonry bearing walls. In general, the lower the roof slope,
the greater the lateral thrust.
v The values for allowable stresses based on the gross
cross-sectional area of masonry units are given in this
table. The gross cross-sectional area is the actual area
of a section perpendicular to the direction of the load,
without subtraction of the core areas of hollow masonry
units.
The flexural strength of surface-bonded walls is about
the same as conventional masonry with mortar joints. In
the vertical direction, where walls are supported top and
bottom, Table 2109.2.3.1 allows a maximum flexural
tensile stress of 18 psi (0.12 MPa) based on the gross
area. In the horizontal direction, where walls span laterally between supports, a maximum flexural stress of 30
psi (0.21 MPa) is permitted based on the gross area
when units are dry stacked in running bond.
The shear strength of surface-bonded walls is less
than that of conventional, mortar-jointed walls. This table allows a shear strength of 10 psi (0.069 MPa) based
on the gross area.
2109.2.3 Surface-bonded walls. Dry-stacked, surface-bonded concrete masonry walls shall comply with the requirements of this code for masonry wall construction, except
where otherwise noted in this section.
2109.2.3.2 Construction. Construction of dry-stacked, surface-bonded masonry walls, including stacking and leveling
of units, mixing and application of mortar and curing and protection shall comply with ASTM C 946.
v Dry-stacked, surface-bonded masonry walls consist of
courses of concrete masonry units without mortar joints
assembled to form unreinforced walls. Both sides of the
walls are coated with a 1/16- to 1/8- inch-thick layer (1.6 to
3.2 mm) of cementitious mortar reinforced with glass fibers capable of increasing the tensile strength of the
masonry and unifying the construction.
v The construction of dry-stacked, surface-bonded walls
must conform to the requirements of ASTM C 946.
It is not practical to construct the horizontal surface of
a wall footing or foundation level enough to receive the
base (first) course of masonry without additional leveling. Therefore, it is customary to lay the base course of
masonry on a mortar bed so that the remainder of the
dry-stacked units will be erected level. As the units are
erected, their ends should be butted together as tightly
as possible.
2109.2.3.1 Strength. Dry-stacked, surface-bonded concrete
masonry walls shall be of adequate strength and proportions to
21-44
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
If the bearing surfaces of the concrete units are not
ground smooth and flat, shims may be required between the units to erect the wall plumb and level. Such
shims should be of metal, mortar, wood or plastic.
Because dry-stacked walls have no mortar joints, it is
not possible to use horizontal steel joint reinforcement
to reduce the size of cracks associated with temperature and moisture movements. Reinforced bond beams
and sufficient control joints in surface-bonded masonry
can be used to reduce the widths of such cracks.
The joints of dry-stacked units are tight, with no space
for connectors to be embedded in the wall. The face
shells or cross webs of such concrete masonry units
therefore, should be notched or depressed to accommodate ties and anchors that must be embedded in
grout.
Packaged dry-bonding mortar should be mixed with
water at the job site in accordance with ASTM C 946 or
the manufacturer’s recommendations, including curing
and protection procedures after application of the material. Surface-bonding mortars are usually applied by
hand troweling to thicknesses between 1/16 and 1/8 inch
(1.6 to 3.2 mm). While they may also be sprayed on, this
is usually followed by hand or mechanical troweling to
obtain the desired finish.
2109.3 Compressive stress requirements.
v This section applies to empirically designed masonry and,
as with the other empirical design requirements of Section
2109, not to masonry designed by the engineered approaches of Sections 2107 and 2108.
Vertical dead and live loads, as required in Chapter 16,
encompass a wide range of possibilities, as does the conceivable configuration of supported floor spans. Consequently, specifying empirical minimum sizes that would
account for all vertical loading and span conditions would
be impractical. Section 2109.3 contains an empirical compressive stress design procedure for single- and multiwythe masonry addressing actual required loading and
resulting in minimum areas of masonry to resist vertical
loads.The design is based on an average compressive
stress on the gross cross-sectional area, using specified
instead of nominal dimensions.
The result is a way of sizing and proportioning masonry
without complete engineering analysis and design. The
required areas are intended to be conservative with respect to engineered design and, along with the other empirical design provisions, to adequately address buildings
and elements permitted to be empirically designed by the
provisions of Section 2109.
2109.3.1 Calculations. Compressive stresses in masonry due
to vertical dead plus live loads, excluding wind or seismic
loads, shall be determined in accordance with Section
2109.3.2.1. Dead and live loads shall be in accordance with
Chapter 16, with live load reductions as permitted in Section
1607.9.
v This section identifies the vertical design loads that must
be used in calculating average compressive stresses. The
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2109.3 – 2109.3.2.1
required dead plus live loads are intended to include all
loads except wind and seismic loads. Design roof loads
given in Chapter 16 are required, including applicable design snow loads.
Effects of wind and seismic forces on empirically designed masonry structures are addressed by the lateral
stability requirements of Section 2109.2 and by the seismic, wind and building height limitations of Section
2109.1.1.
2109.3.2 Allowable compressive stresses. The compressive
stresses in masonry shall not exceed the values given in Table
2109.3.2. Stress shall be calculated based on specified rather
than nominal dimensions.
v The maximum permitted compressive stresses on the
gross cross-sectional area are given in Table 2109.3.2.
Calculation of gross-area compressive stresses is discussed in the commentary to Section 2109.3.2.1. Section 2109.3.2 requires the use of specified dimensions
(see also the commentary for the definition of “Dimensions” in Section 2102.1).
TABLE 2109.3.2. See page 21-46.
v The compressive strength of the unit, as well as the mortar
type used, limit the allowable compressive stress on the
gross area.
2109.3.2.1 Calculated compressive stresses. Calculated
compressive stresses for single wythe walls and for
multiwythe composite masonry walls shall be determined by
dividing the design load by the gross cross-sectional area of the
member. The area of openings, chases or recesses in walls shall
not be included in the gross cross-sectional area of the wall.
v Using the vertical design load required by Section
2109.3.1, the compressive stress on the gross
cross-sectional area of the masonry must be calculated.
Gross cross-sectional area is illustrated in Figure
2102.1(3) for two single-wythe wall examples. Specified
(not nominal) dimensions are used and mortared head
joints are included. Cores are not required to be subtracted. Other openings in the wall, including chases
and recesses, are required to be subtracted.
The calculated compressive stress is the total required design load divided by the gross cross-sectional
area, as illustrated in Figure 2109.3.2.1(1) for a single-wythe wall. The dead weight of the masonry units is
part of the total required design load. The calculated
compressive stresses are not to exceed the allowable
values listed in Table 2109.3.2.
The allowable compressive stresses for masonry directly under concentrated loads (bearing stresses) are
recommended in the commentary to ACI 530/ASCE
5/TMS 402: 125 percent of the Table 2109.3.2 value if
the load acts on the full wall thickness; or 150 percent of
the Table 2109.3.2 value if the load acts on concentrically placed bearing plates greater than one-half, but
less than the full supporting area. Concentrated loads
on load-bearing walls transmitted from beams, girders
21-45
2109.3.2.2
MASONRY
or other structural elements normally bear on units of
solid masonry or on hollow masonry units with
grout-filled cores at least 4 inches (102 mm) high.
Bearing plates are often used to distribute concentrated loads and to prevent damage to the bearing areas of the supporting masonry. Masonry bond beams
can also be used for this purpose.
Concentrated loads must be distributed over an area
whose length cannot exceed the center-to-center distance between loads, nor one-half of the wall height
[see Figure 2109.3.2.1(2)]. Loads are not to be distributed across continuous vertical joints, such as expansion or control joints in masonry walls, or across head
joints in stack bond construction. For large concentrated loads, masonry pilasters may be required.
2109.3.2.2 Multiwythe walls. The allowable stress shall be as
given in Table 2109.3.2 for the weakest combination of the
units used in each wythe.
v Multiwythe masonry walls are often constructed with
units having different mechanical properties. An example of a multiwythe wall is a composite 8-inch (204 mm)
nominal thickness wall using Type S mortar, consisting
of one wythe of 4-inch-wide (102 mm) common brick
and one wythe of 4-inch-wide (102 mm) lightweight concrete block, bonded together with required joint reinforcement and having completely filled collar joints.
In this example, if the compressive strength of the
concrete masonry unit is less than that of the common
brick, the allowable compressive stress for both wythes
is to be based on the strength of the concrete masonry
TABLE 2109.3.2
ALLOWABLE COMPRESSIVE STRESSES FOR EMPIRICAL DESIGN OF MASONRY
CONSTRUCTION; COMPRESSIVE
STRENGTH OF UNIT
GROSS AREA (psi)
ALLOWABLE COMPRESSIVE
STRESSESa GROSS CROSS-SECTIONAL AREA (psi)
Type M or S mortar
Type N mortar
Solid masonry of brick and other solid units of clay or
shale; sand-lime or concrete brick:
8,000 or greater
4,500
2,500
1,500
350
225
160
115
300
200
140
100
Grouted masonry, of clay or shale; sand-lime or concrete:
4,500 or greater
2,500
1,500
225
160
115
200
140
100
Solid masonry of solid concrete masonry units:
3,000 or greater
2,000
1,200
225
160
115
200
140
100
Masonry of hollow load-bearing units:
2,000 or greater
1,500
1,000
700
140
115
75
60
120
100
70
55
Hollow walls (noncomposite masonry bonded)b
Solid units:
2,500 or greater
1,500
Hollow units
160
115
75
140
100
70
Stone ashlar masonry:
Granite
Limestone or marble
Sandstone or cast stone
720
450
360
640
400
320
Rubble stone masonry
Coursed, rough or random
120
100
For SI:
1 pound per square inch = 0.006895 MPa.
a. Linear interpolation for determining allowable stresses for masonry units having compressive strengths which are intermediate between those given in the table is
permitted.
b. Where floor and roof loads are carried upon one wythe, the gross cross-sectional area is that of the wythe under load; if both wythes are loaded, the gross cross-sectional area is that of the wall minus the area of the cavity between the wythes. Walls bonded with metal ties shall be considered as noncomposite walls unless collar
joints are filled with mortar or grout.
21-46
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2109.4 – TABLE 2109.4.1
unit.
For loading on only one wythe of a composite
(grouted collar joint), multiwythe masonry wall, the
wythes and the collar joint are to be considered part of
the gross cross-sectional area. For loading on only one
wythe of a noncomposite (ungrouted collar joint) multiwythe masonry wall, the gross cross-sectional area is
limited to the area of the wythe under load and the allowable compressive stresses in Table 2109.3.2 are
based on the units and mortar comprising the wythe under load.
The use of the term “composite” refers to
multicomponent masonry members that act as a unit.
Note b of Table 2109.3.2 considers a multiwythe masonry wall to act compositely (monolithically) if it is
bonded with metal ties (or joint reinforcement) and has
completely filled collar joints.
Openings in the wall, including chases and recesses,
are required to be subtracted from the gross wall area,
as stated in Section 2106.2.1.
The design professional is responsible for indicating
in the construction documents the method of lateral
support of masonry walls.
2109.4.1 Intervals. Masonry walls shall be laterally supported
in either the horizontal or vertical direction at intervals not exceeding those given in Table 2109.4.1.
v The requirements of this section prescribe maximum
length or height-to-thickness ratios for locations of lateral
support (see Figure 2109.4.1). Providing lateral support at
the resulting maximum heights increases the buckling capacity to an acceptable level. Spacing of lateral support
must be designed either vertically or horizontally, but not in
both directions.
TABLE 2109.4.1
WALL LATERAL SUPPORT REQUIREMENTS
CONSTRUCTION
2109.4 Lateral support.
v Section 2109.4 contains empirical design provisions for
the spacing of lateral support locations of masonry
walls. Requirements include maximum ratios of wall
length or wall height to wall thickness. The requirements
of this section do not apply when the engineered masonry design method of Section 2101.1.1 is selected.
Compression elements such as columns and walls
may have axial capacities limited by buckling, based on
slenderness effects (which depends on their stiffness
and unsupported length). Limits are also included for
nonbearing walls to account for resistance to
out-of-plane loads.
MAXIMUM WALL LENGTH TO
THICKNESS OR WALL HEIGHT
TO THICKNESS
Bearing walls
Solid units or fully grouted
All others
20
18
Nonbearing walls
Exterior
Interior
18
36
v This table shows maximum length- or height-to-thickness ratios between locations of lateral support. Lateral
support is required to be provided either vertically or
horizontally, but not in both directions.
Figure 2109.4.1 illustrates use of the table for an em-
UNIFORM LOAD FROM ABOVE
TOTAL LOAD RESULTANT
(INCLUDES MASONRY
WEIGHT)
SINGLE-WYTHE
MASONRY WALL
SPECIFIED
LENGTH
DESIGN LOAD
GROSS CROSS-SECTIONAL AREA
SPECIFIED WIDTH
(THICKNESS)
< TABLE 2109.3.2 ALLOWABLE COMPRESSIVE STRESS
GROSS CROSS-SECTIONAL AREA = SPECIFIED LENGTH x SPECIFIED THICKNESS
Figure 2109.3.2.1(1)
ALLOWABLE COMPRESSIVE STRESS FOR AN EMPIRICALLY DESIGNED MASONRY WALL
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-47
2109.4.2
MASONRY
BEARING PLATE
SOLID UNIT
LOAD
LOAD
BEARING WIDTH
RUNNING BOND
LOAD
l'
T
45°
EFFECTIVE l
45°
EFFECTIVE l
EFFECTIVE l < l'
EFFECTIVE l
EFFECTIVE l < BEARING WIDTH + 4T
For SI: 1 degree = .01745 rad.
Figure 2109.3.2.1(2)
ASSUMED DISTRIBUTION OF COMPRESSIVE STRESS UNDER CONCENTRATED LOAD
pirically designed masonry building. As shown, the
height is measured between points of lateral support.
ROOF DIAPHRAGM
HEIGHT
FLOOR DIAPHRAGM
2109.4.2 Thickness. Except for cavity walls and cantilever
walls, the thickness of a wall shall be its nominal thickness measured perpendicular to the face of the wall. For cavity walls, the
thickness shall be determined as the sum of the nominal thicknesses of the individual wythes. For cantilever walls, except for
parapets, the ratio of height-to-nominal thickness shall not exceed six for solid masonry or four for hollow masonry. For parapets, see Section 2109.5.5.
LENGTH
PILASTER
CROSS WALL
CROSS WALL
ANCHORED ROOF
ANCHORAGE
21-48
HEIGHT
NOMINAL WIDTH
(THICKNESS)
ANCHORAGE
ANCHORED FLOOR
COMPOSITE (MONOLITHIC)
MASONRY WALL
ANCHORAGE
ANCHORAGE
LENGTH
HEIGHT
ANCHORED CROSS WALL
OR
MASONRY WALL
ANCHORAGE
HEIGHT
v The nominal thickness or the sum of the nominal thicknesses is used in determining the wall thickness for use
in Table 2109.4.1. Figure 2102.1(5) illustrates nominal
versus specified thickness of a particular concrete masonry unit. Nominal dimensions are discussed in the
commentary to Section 2102.1 (see the definition of “Dimensions”).
The use of the nominal thickness is permitted for calculating thickness ratios for empirical design. In contrast, the engineered design method uses the rational
Euler buckling equation and the accuracy of specified
dimensions is appropriately required. Table 2109.4.1 is
intended, however, to produce conservative results with
respect to the engineered method in most cases.
For cavity walls, the adjacent wythes do not act together because of the absence of a shear connection.
Thus, the wall thickness consists of only the sum of the
wythes.
This section does not include retaining walls, which
NOMINAL WIDTH
(THICKNESS)
LENGTH
≤ TABLE 2109.4.1 VALUE
THICKNESS
ANCHORAGE
PLAN VIEW
HEIGHT
≤ TABLE 2109.4.1 VALUE
THICKNESS
LENGTH
< TABLE 2109.4.1 VALUE
W 1 + W2
SECTION VIEW
W1
W2
Figure 2109.4.1
LATERAL SUPPORT REQUIREMENTS FOR
EMPIRICALLY DESIGNED MASONRY WALLS
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
must comply with the requirements of Chapter 18. For
definitions of “Solid” and “Hollow” masonry, refer to Section 2102.1.
Free-standing cantilever walls have a lower allowable
height-to-thickness ratio because of the lack of lateral
support at the free (unsupported) end. Parapets are
subject to the more restrictive requirements of Section
2109.5.5 because of their location and exterior
exposure.
2109.4.3 Support elements. Lateral support shall be provided
by cross walls, pilasters, buttresses or structural frame members
when the limiting distance is taken horizontally, or by floors,
roofs acting as diaphragms or structural frame members when
the limiting distance is taken vertically.
v Lateral support points complying with the requirements
of this section are achieved by required anchorage
complying with Section 2109.7.
The code requires only one direction of span for lateral support, either vertical or horizontal. The lateral
support of masonry walls can be achieved by floors or
roofs when the limiting distance is measured vertically,
or by columns, buttresses (pilasters) or cross walls
when the limiting distance is measured horizontally.
A masonry pier is an isolated column designed to
support vertical loads. A pilaster is a masonry column
integrally bonded to a wall.
A buttress is a pilaster whose outside edge (face running in the same direction as the wall) slants toward the
wall and whose horizontal cross section increases from
top to bottom. Buttresses are used mainly for out-of-plane
lateral support of high walls. Both pilasters and buttresses
may project out from one or both faces of the wall.
For empirical design, solid bearing walls are permitted to span 20 times their thickness between supports,
while hollow walls or walls of hollow masonry units can
span 18 times their thickness. For example, a 16-inch
(406 mm) hollow block wall or wall constructed with hollow units can have an unsupported height or length of
24 feet (7315 mm) [18 times 1.33 feet (405 mm)].
2109.5 Thickness of masonry. Minimum thickness requirements shall be based on nominal dimensions of masonry.
2109.4.3 – 2109.5.5.1
compared to the results achieved from a working stress
analysis.
2109.5.2 Minimum thickness. The minimum thickness of masonry bearing walls more than one story high shall be 8 inches
(203 mm). Bearing walls of one-story buildings shall not be less
than 6 inches (152 mm) thick.
v The minimum thicknesses required in this section are
nominal thicknesses (in accordance with the definition in
Section 2102.1) and apply to bearing walls. Like the measurement of thickness in Section 2109.4, the space between cavity walls and multiwythe, noncomposite walls is
to be excluded when determining wall thickness.
2109.5.3 Rubble stone walls. The minimum thickness of rough
or random or coursed rubble stone walls shall be 16 inches (406
mm).
v Rubble stone walls are composed of stone masonry
having irregularly shaped units bonded by mortar. The
greater thickness required for these walls is justified by
this irregularity. Accordingly, Table 2109.3.2 permits relatively low compressive stresses for this material. Nominal thickness in this case is the average thickness. This
section is not applicable to ashlar masonry (rectangular
units).
2109.5.4 Change in thickness. Where walls of masonry of hollow units or masonry bonded hollow walls are decreased in
thickness, a course or courses of solid masonry shall be interposed between the wall below and the thinner wall above, or
special units or construction shall be used to transmit the loads
from face shells or wythes above to those below.
v Where hollow walls are decreased in thickness, one or
more courses of solid masonry are to be placed between the thicker wall below and the thinner wall above.
Alternatively, special construction can be introduced to
transmit the load from the wall above to the supporting
wall below. For walls constructed with concrete masonry units, a bond beam as thick as the lower wall may
be placed between the two wall sections.
v Section 2109.5 provides requirements for minimum
nominal thicknesses of empirically designed walls of
masonry, including rubble stone (see the definition of
“Dimensions”). Changes in thickness and parapet walls
are also included in this section.
2109.5.5 Parapet walls.
2109.5.1 Thickness of walls. The thickness of masonry walls
shall conform to the requirements of Section 2109.5.
2109.5.5.1 Minimum thickness. Unreinforced parapet walls
shall be at least 8 inches (203 mm) thick, and their height shall
not exceed three times their thickness.
v Section 2109.5.1 contains provisions for minimum nominal thicknesses of empirically designed masonry walls.
The requirements of this section do not apply when engineered masonry design is used.
The MSJC has concluded that the minimum thickness ratios listed in Section 2109.4.1 (which are derived
from ANSI A41.1) are not always conservative when
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
v Parapet walls are cantilever walls located above the
roof line that are typically exposed to weather on both
faces; therefore, they may require special consideration.
v Because of their exposure conditions and the hazard associated with unreinforced parapets, a minimum thickness
of 8 inches (203 mm) and a maximum height-to-thickness
ratio of 3:1 is required. These requirements are minimums
and thicker parapets or smaller height-to-thickness ratios
may be necessary.
21-49
2109.5.5.2 – 2109.6.2.1
MASONRY
2109.5.5.2 Additional provisions. Additional provisions for
parapet walls are contained in Sections 1503.2 and 1503.3.
v See the commentary to Sections 1504.2, 1504.3 and
1504.4 regarding the application of these provisions to
parapets.
2109.5.6 Foundation walls. Foundation walls shall comply
with the requirements of Sections 2109.5.6.1 and 2109.5.6.2.
v Masonry foundation walls must comply with Section
1805.5 if the requirements of this section cannot be met.
2109.5.6.1 Minimum thickness. Minimum thickness for foundation walls shall comply with the requirements of Table
2109.5.6.1. The provisions of Table 2109.5.6.1 are only applicable where the following conditions are met:
1. The foundation wall does not exceed 8 feet (2438 mm) in
height between lateral supports,
2. The terrain surrounding foundation walls is graded to
drain surface water away from foundation walls,
3. Backfill is drained to remove ground water away from
foundation walls,
4. Lateral support is provided at the top of foundation walls
prior to backfilling,
5. The length of foundation walls between perpendicular
masonry walls or pilasters is a maximum of three times
the basement wall height,
6. The backfill is granular and soil conditions in the area are
nonexpansive, and
7. Masonry is laid in running bond using Type M or S
mortar.
v This section provides empirical criteria for foundation
walls that are based on similar requirements in the
MSJC Code. It is necessary to satisfy the seven listed
conditions in order to use this approach.
TABLE 2109.5.6.1
FOUNDATION WALL CONSTRUCTION
NOMINAL WALL
THICKNESS
(inches)
MAXIMUM DEPTH OF
UNBALANCED BACKFILL
(feet)
Hollow unit masonry
8
10
12
5
6
7
Solid unit masonry
8
10
12
5
7
7
Fully grouted masonry
8
10
12
7
8
8
WALL
CONSTRUCTION
For SI:
1 inch = 25.4 mm, 1 foot = 304.8 mm.
v The minimum foundation wall thickness can be established from this table based on the depth of fill that is
supported, as well as the proposed wall construction.
21-50
2109.5.6.2 Design requirements. Where the requirements of
Section 2109.5.6.1 are not met, foundation walls shall be designed in accordance with Section 1805.5.
v If the conditions of Section 2109.5.6.1 cannot be met,
the more general requirements for foundation walls in
Chapter 18 must be complied with.
2109.6 Bond.
v Section 2109.6 contains provisions for bonding adjacent wythes of empirically designed multiwythe masonry walls. The requirements of this section do not apply to engineered masonry design methods of Section
2107 or 2108.
2109.6.1 General. The facing and backing of multiwythe masonry walls shall be bonded in accordance with Section
2109.6.2, 2109.6.3 or 2109.6.4.
v This section establishes the requirements and methods
of bonding together the facing and backing of adjacent
wythes of multiwythe masonry walls. The use of masonry units, nonadjustable metal ties, adjustable metal
ties and metal joint reinforcement as bonding elements
is provided for in this section.
Bonding increases structural integrity, including load
transfer between adjacent wythes and across head and
collar joints. The requirements include both transverse
(through-wall) and longitudinal (in-wall) bonding. Longitudinal bonding is provided for in Section 2109.5, with
requirements for running bond and stack bond.
Adjacent wythes of multiwythe masonry walls are
usually brick-to-brick, brick-to-block or block-to-block.
Collar joints are usually 3/8 to 4 inches (9.5 to 102 mm)
thick.
Adjacent wythes of multi-wythe masonry walls are
considered composite (monolithic) when connected by
metal ties or joint reinforcement and by a collar joint solidly filled with mortar or grout. Accordingly, Note b of Table 2109.3.2 requires completely filled collar joints if adjacent wythes bonded with metal ties are to be
considered composite (monolithic) for empirical compressive stress design.
2109.6.2 Bonding with masonry headers.
v Masonry headers (bonders) are permitted to be used to
connect adjacent wythes, in accordance with this section.
Differential thermal movement, especially at exterior walls,
can crack masonry bonders. Metal ties or joint reinforcement are more ductile and are recommended at these locations. Walls having the specified masonry bonders are
considered composite (monolithic). Header requirements
are based on successful past performance.
2109.6.2.1 Solid units. Where the facing and backing (adjacent
wythes) of solid masonry construction are bonded by means of
masonry headers, no less than 4 percent of the wall surface of
each face shall be composed of headers extending not less than 3
inches (76 mm) into the backing. The distance between adjacent
full-length headers shall not exceed 24 inches (610 mm) either
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
vertically or horizontally. In walls in which a single header does
not extend through the wall, headers from the opposite sides
shall overlap at least 3 inches (76 mm), or headers from opposite
sides shall be covered with another header course overlapping
the header below at least 3 inches (76 mm).
v Solid masonry units are defined in Section 2102.1. The
4-percent requirement applies to each surface of the
wall and 24-inch (610 mm) spacing is required in both
horizontal and vertical directions. Spacing is measured
between the nearest surfaces of masonry units. The
3-inch (76 mm) overlap is a projected measurement,
since headers are spaced a maximum of 24 inches (610
mm) vertically.
Bonding requirements for solid units are less restrictive than for hollow units because of the greater
cross-sectional area crossing the collar joint.
2109.6.2.2 – 2109.6.3
Adjacent wythes bonded with metal ties or joint reinforcement are considered composite (monolithic) only if
the collar joint between them is completely filled with
mortar or grout.
CROSS WIRE
LONGITUDINAL
WIRE
CROSS WIRE
TYPICAL JOINT REINFORCEMENT
(LADDER TYPE)
LONGITUDINAL
WIRE
TYPICAL JOINT REINFORCEMENT
(TRUSS TYPE)
BENT
END
TH
NG
LE
2109.6.2.2 Hollow units. Where two or more hollow units are
used to make up the thickness of a wall, the stretcher courses
shall be bonded at vertical intervals not exceeding 34 inches
(864 mm) by lapping at least 3 inches (76 mm) over the unit below, or by lapping at vertical intervals not exceeding 17 inches
(432 mm) with units that are at least 50 percent greater in thickness than the units below.
HOOK END
STEEL CONNECTOR
(ANCHOR)
TYPICAL WALL TIE
(Z-WIRE TYPE)
v Hollow masonry units are defined in Section 2102.1. An
entire course of headers is required at the stated vertical spacing. Spacing is measured between the nearest
surfaces of masonry units. The halved spacing of 17
inches (432 mm) is permitted for units having twice the
thickness, because of the greater cross-sectional area
crossing the collar joint. Bonding requirements for hollow units are more restrictive than for solid units because of the smaller cross-sectional area crossing the
collar joint.
2109.6.2.3 Masonry bonded hollow walls. In masonry bonded
hollow walls, the facing and backing shall be bonded so that not
less than 4 percent of the wall surface of each face is composed
of masonry bonded units extending not less than 3 inches (76
mm) into the backing. The distance between adjacent bonders
shall not exceed 24 inches (610 mm) either vertically or horizontally.
Figure 2109.6.3(1)
TYPICAL MASONRY ACCESSORIES
36" MAX. HORIZONTAL (RECOMMENDED)
24" MAX. VERTICAL
2 2/3 SQ. FT. MAX.
PREFABRICATED JOINT REINFORCEMENT (CROSS WIRES, MINIMUM WIRE SIZE W1.7)
24" MAX. VERTICAL
36" MAX. HORIZONTAL
v This section prescribes procedures for bonding hollow
walls using masonry units.
4 1/2 SQ.FT. MAX.
NONADJUSTABLE WALL TIES (WIRE SIZE W2.8)
2109.6.3 Bonding with wall ties or joint reinforcement.
v Figure 2109.6.3(1) illustrates typical masonry accessories. Shown are ladder-type and truss-type joint reinforcement and a “Z” wire wall tie. The spacing requirements given in this section are illustrated in Figure
2109.6.3(2). Strength and durability requirements for
metal ties and joint reinforcement are given in Section
2103.11. Wall ties are required to be placed in accordance with Section 2104.1.3.
Metal wall ties or joint reinforcement provide a more
ductile connection between adjacent wythes than do
masonry headers. The size, spacing and number of ties
required in this section are based on experience.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
BENT
END
16" MAX. HORIZONTAL
1.77 SQ. FT. MAX.
16" MAX. VERTICAL
ADJUSTABLE TIES
For SI:
1 inch = 25.4 mm, 1 square foot = .0929 m2.
Figure 2109.6.3(2)
EMPIRICAL REQUIREMENTS FOR BONDING
MULTIWYTHE WALLS WITH TIES OR JOINT
REINFORCEMENT
21-51
2109.6.3.1 – 2109.6.5.1
2109.6.3.1 Bonding with wall ties. Except as required by Section 2109.6.3.1.1, where the facing and backing (adjacent
wythes) of masonry walls are bonded with wire size W2.8
(MW18) wall ties or metal wire of equivalent stiffness embedded in the horizontal mortar joints, there shall be at least one
metal tie for each 41/2 square feet (0.42 m2) of wall area. The
maximum vertical distance between ties shall not exceed 24
inches (610 mm), and the maximum horizontal distance shall
not exceed 36 inches (914 mm). Rods or ties bent to rectangular
shape shall be used with hollow masonry units laid with the cells
vertical. In other walls, the ends of ties shall be bent to 90-degree
(1.57 rad) angles to provide hooks no less than 2 inches (51 mm)
long. Wall ties shall be without drips. Additional bonding ties
shall be provided at all openings, spaced not more than 36
inches (914 mm) apart around the perimeter and within 12
inches (305 mm) of the opening.
v Requirements for spacing of nonadjustable wall ties are
shown in Figure 2109.6.3(2). The minimum wire size is
W2.8. Where wythes of hollow units are bonded and cores
are required to be vertical, rectangular-shaped ties are required. “Z” ties, illustrated in Figure 2109.6.3(1), are used
in other applications. Drips on wall ties can adversely affect the tie strength and are, therefore, prohibited.
2109.6.3.1.1 Bonding with adjustable wall ties. Where the
facing and backing (adjacent wythes) of masonry are bonded
with adjustable wall ties, there shall be at least one tie for each
1.77 square feet (0.164 m2) of wall area. Neither the vertical nor
horizontal spacing of the adjustable wall ties shall exceed 16
inches (406 mm). The maximum vertical offset of bed joints
from one wythe to the other shall be 11/4 inches (32 mm). The
maximum clearance between connecting parts of the ties shall
be 1/16 inch (1.6 mm). When pintle legs are used, ties shall have at
least two wire size W2.8 (MW18) legs.
v Spacing requirements for bonding with adjustable ties
are shown in Figure 2109.6.3(2) and are more restrictive because of the lower stiffness of those ties. A single
tie of the pintle- and eye-type is required to have two
legs. The maximum clearance between the eye and
pintle is 1/16 inch (1.6 mm). Figures 2109.6.3.1.1 (1), (2)
and (3) show requirements for adjustable anchors.
2109.6.3.2 Bonding with prefabricated joint reinforcement.
Where the facing and backing (adjacent wythes) of masonry are
bonded with prefabricated joint reinforcement, there shall be at
least one cross wire serving as a tie for each 22/3 square feet (0.25
m2) of wall area. The vertical spacing of the joint reinforcing
shall not exceed 24 inches (610 mm). Cross wires on prefabricated joint reinforcement shall not be less than W1.7 (MW11)
and shall be without drips. The longitudinal wires shall be embedded in the mortar.
v Truss and ladder-type joint reinforcement is illustrated
in Figures 2102.1(4), 2109.6.3(1), 2109.6.3.1.1(1) and
2109.6.3.1.1(2). Ladder-type joint reinforcement better
accommodates differential movement between wythes.
Cross wires are required to have a minimum wire size of
W1.7 for the transfer of stresses between adjacent
wythes across the collar joint. Cross wires are permitted
21-52
MASONRY
to be plain, while longitudinal wires are required to be
deformed for increased bond strength.
2109.6.4 Bonding with natural or cast stone.
v Because of the irregularity of mortar joints permitted
with coursed, random or rough stone masonry, as well
as the need for peripheral mortar area in through-wall
bonding units, metal ties do not adequately bond and
are not required in this type of construction.
2109.6.4.1 Ashlar masonry. In ashlar masonry, bonder units,
uniformly distributed, shall be provided to the extent of not less
than 10 percent of the wall area. Such bonder units shall extend
not less than 4 inches (102 mm) into the backing wall.
v Ashlar is often classified as either coursed or random.
Bonding requirements apply equally to both types. The
10-percent requirement applies to one wall surface only.
The “uniform distribution” requirement is intended to allow for slight deviations necessary for the nonmodular
units typically encountered.
2109.6.4.2 Rubble stone masonry. Rubble stone masonry 24
inches (610 mm) or less in thickness shall have bonder units
with a maximum spacing of 36 inches (914 mm) vertically and
36 inches (914 mm) horizontally, and if the masonry is of
greater thickness than 24 inches (610 mm), shall have one
bonder unit for each 6 square feet (0.56 m2) of wall surface on
both sides.
v Rubble stone masonry is required to be through bonded
using stones placed at a maximum spacing of 3 feet
(914 mm) vertically and horizontally. Where the wall is
more than 24 inches (610 mm) thick, at least one bond
unit is required for each 6 square feet (0.56 m2) of wall
surface on both sides.
2109.6.5 Masonry bonding pattern.
v Masonry may be constructed with a variety of bond patterns to provide a variety of decorative appearances.
Because some of these bond patterns are stronger than
others, two broad categories have been established to
describe them. Section 2109.5.1 applies to masonry
laid in running bond. Section 2109.6.5.2 applies to masonry laid in “other than running bond,” which in that
section is referred to as “stack bond,” although that term
can also be used to describe a very specific bond pattern in which the head joints are aligned continuously
from course to course, rather than being offset. See the
definitions of “Running bond” and “Stack bond” in Section 2102.1 and related commentary.
2109.6.5.1 Masonry laid in running bond. Each wythe of masonry shall be laid in running bond, head joints in successive
courses shall be offset by not less than one-fourth the unit length
or the masonry walls shall be reinforced longitudinally as required in Section 2109.6.5.2.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2109.6.5.2 – 2109.7.1
v The requirement for running bond is illustrated in Figure
2102.1(6). The minimum overlap is intended to provide
structural continuity across head joints.
2109.6.5.2 Masonry laid in stack bond. Where unit masonry is
laid with less head joint offset than in Section 2109.6.5.1, the
minimum area of horizontal reinforcement placed in mortar bed
joints or in bond beams spaced not more than 48 inches (1219
mm) apart, shall be 0.0003 times the vertical cross-sectional
area of the wall.
SECTION
T
5/8 INCH MIN.
OR T/2 MAX.
v Where the overlap required for running bond, as illustrated in Figure 2102.1(6), is not provided, additional
structural continuity must be provided across head
joints in accordance with this section. Each mortar joint
or bond beam is required to have the minimum stated
reinforcement to provide distributed reinforcement in
the wall.
A) TRUSS TYPE
T
5/8 INCH MIN.
OR T/2 MAX.
2109.7 Anchorage.
B) LADDER TYPE
For SI:
2109.7.1 General. Masonry elements shall be anchored in accordance with Sections 2109.7.2 through 2109.7.4.
1 inch = 25.4 mm.
VERTICAL SECTION
Figure 2109.6.3.1.1(2)
ADJUSTABLE ASSEMBLY DETAILS
MAX. 1 1/4″
v This section contains provisions for anchorage of empirically designed masonry elements at locations of lateral support, including intersecting walls, floors, roofs
and adjoining structural framing. The requirements of
this section do not apply to the engineered masonry design methods of Sections 2107 and 2108.
3/16″ WIRE
D2
D1
PLAN VIEW
D2 -D1 = MECH. PLAY = 1/16″
EYE UNIT
A) LADDER TYPES
B) TRUSS TYPES
PINTLE UNIT
For SI: 1 inch = 25.4 mm.
Figure 2109.6.3.1.1(1)
ADJUSTABLE JOINT REINFORCEMENT ASSEMBLIES
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
Figure 2109.6.3.1.1(3)
ADJUSTABLE WALL TIES
21-53
2109.7.2 – 2109.7.2.2
MASONRY
v This section establishes the requirements and methods
of anchoring masonry walls to intersecting walls, floors
and roofs. This section covers anchoring requirements
for masonry bonders and for metal ties and anchors.
Anchorage in accordance with this section is required
for empirically designed masonry. Anchorage provisions address empirical lateral load resistance, but not
the vertical load resistance of the connection, floor or
roof system. The vertical load resistance of the connection, floor or roof system, including permitted spans,
bearing requirements and bracing, must comply with
applicable code requirements. The empirical provisions
in this chapter do not address elements with horizontal
spans, such as wood, floor decks, roof systems or concrete or steel beams.
2109.7.2 Intersecting walls. Masonry walls depending upon
one another for lateral support shall be anchored or bonded at locations where they meet or intersect by one of the methods indicated in Sections 2109.7.2.1 through 2109.7.2.5.
v Where required by the lateral bracing requirements in
Section 2109.4, intersecting walls and partitions must
be anchored together by any of the methods described
in the sections that follow (see Figure 2109.7.2). These
requirements, however, do not prohibit other methods
for connecting intersecting walls.
For example, long walls, by design, often require control joints or expansion joints at cross walls. The construction details for these walls differ considerably from
walls that are required to be anchored or bonded
monolithically.
Intersecting walls, such as tees and corners, may be
tied together using interlocking masonry units or heavy
metal ties placed in the bed joints.
2109.7.2.1 Bonding pattern. Fifty percent of the units at the intersection shall be laid in an overlapping masonry bonding pattern, with alternate units having a bearing of not less than 3
inches (76 mm) on the unit below.
v Masonry bonding requires that at least 50 percent of the
masonry units cross at the juncture of the walls as bonding units. The units must be laid with a 3-inch (76 mm)
minimum bearing. Figure 2109.7.2 shows typical brick
walls bonded at a tee intersection and a corner. While
these coursings are common, others are possible.
2109.7.2.2 Steel connectors. Walls shall be anchored by steel
connectors having a minimum section of 1/4 inch (6.4 mm) by
11/2 inches (38 mm), with ends bent up at least 2 inches (51 mm)
or with cross pins to form anchorage. Such anchors shall be at
least 24 inches (610 mm) long and the maximum spacing shall
be 48 inches (1219 mm).
v Rigid steel connectors must be used at vertical intervals
of 4 feet (1219 mm) or less. For this type of anchorage,
the most commonly used fastener is a steel strip with
cross-sectional dimensions not less than 1/4 by 11/2
inches (6.4 by 38 mm) in lengths of 2 feet (610 mm) or
more and with 2-inch (51 mm) hooked ends [see Figure
2109.6.3(1)]. Figure 2109.7.2 shows a tee and corner
connection made with steel connectors.
ALTERNATE COURSES SHOWN
1/2 BRICK UNIT
1/2 BRICK UNIT
BONDING UNITS
(50% OF UNITS MIN.)
BONDING
UNITS
(50% OF UNITS MIN.)
ALTERNATE COURSES SHOWN
8" NOM. WALL
1/4" x 1 1/2" x 24"
STEEL ANCHOR
AT 4 FEET O.C. VERTICALLY
30" MIN.
JOINT REINFORCEMENT
8" O.C. VERTICALLY MAX.
WIRE SIZE W1.7
30" MIN.
30" MIN.
60" MIN.
EACH END BENT-UP 2"
For SI:
1 inch = 25.4 mm.
Figure 2109.7.2
ANCHORAGE OF INTERSECTING WALLS
21-54
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2109.7.2.3 Joint reinforcement. Walls shall be anchored by
joint reinforcement spaced at a maximum distance of 8 inches
(203 mm). Longitudinal wires of such reinforcement shall be at
least wire size W1.7 (MW 11) and shall extend at least 30 inches
(762 mm) in each direction at the intersection.
v Figure 2109.7.2 shows a tee and corner connection
made with joint reinforcement. Prefabricated joint reinforcement made for that purpose is commonly used.
Joint reinforcement is spaced not more than 8 inches
(204 mm) vertically.
The ladder-type joint reinforcement shown is made
with 3/16-inch-diameter (4.8 mm) deformed side bars
cross connected with a minimum wire size of W1.7.
2109.7.2.4 Interior nonload-bearing walls. Interior
nonload-bearing walls shall be anchored at their intersection, at
vertical intervals of not more than 16 inches (406 mm) with joint
reinforcement or 1/4-inch (6.4 mm) mesh galvanized hardware
cloth.
v Where interior nonload-bearing masonry walls or partitions intersect, they may be connected by bonders described in Section 2109.7.2.1 or, if constructed separately, by joint reinforcement or 1/4-inch (6.4 mm)
galvanized steel mesh spaced vertically at a maximum
interval of 16 inches (406 mm).
2109.7.2.5 Ties, joint reinforcement or anchors. Other metal
ties, joint reinforcement or anchors, if used, shall be spaced to
provide equivalent area of anchorage to that required by this section.
v Truss-type, prefabricated metal ties and steel strip anchors bent at the ends can be hooked into vertical mortar joints or embedded in grout-filled cores of concrete
block units. Other methods of reinforcement can be
used if their cross-sectional area and distribution are
equivalent.
2109.7.3 Floor and roof anchorage. Floor and roof diaphragms providing lateral support to masonry shall comply with
the live loads in Section 1607.3 and shall be connected to the
masonry in accordance with Sections 2109.7.3.1 through
2109.7.3.3.
v Where the lateral support locations required in Section
2109.4 are provided by intersecting floors or roofs, the
minimum anchorage requirements of this section apply.
The specified anchorage is intended to transfer shear
between a floor or roof diaphragm and the wall, as well
as provide locations of lateral support.
This section does not address vertical load resistance
of floors or roofs. The connections required by the loads
transferred from floors and roofs must be in accordance
with applicable requirements for those elements, including required design loads in Chapter 16. The minimum
requirements stated here do not address floor and roof
loads to be resisted by the connection.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2109.7.2.3 – 2109.8
2109.7.3.1 Wood floor joists. Wood floor joists bearing on masonry walls shall be anchored to the wall at intervals not to exceed 72 inches (1829 mm) by metal strap anchors. Joists parallel
to the wall shall be anchored with metal straps spaced not more
than 72 inches (1829 mm) o.c. extending over or under and secured to at least three joists. Blocking shall be provided between
joists at each strap anchor.
v Anchorage with metal straps is specified by this section.
Blocking is required for stability against rotation of joists
parallel to the wall. Strength and material requirements
for metal straps are specified in Section 2103.11.
2109.7.3.2 Steel floor joists. Steel floor joists bearing on masonry walls shall be anchored to the wall with 3/8-inch (9.5 mm)
round bars, or their equivalent, spaced not more than 72 inches
(1829 mm) o.c. Where joists are parallel to the wall, anchors
shall be located at joist bridging.
v The strength and material requirements for 3/8-inch (9.5
mm) round bars are specified in Section 2103.11. The
requirements for steel joist construction, including materials, design, load-bearing capacity and cross bridging, are in Chapter 22.
2109.7.3.3 Roof diaphragms. Roof diaphragms shall be anchored to masonry walls with 1/2-inch-diameter (12.7 mm) bolts,
72 inches (1829 mm) o.c. or their equivalent. Bolts shall extend
and be embedded at least 15 inches (381 mm) into the masonry,
or be hooked or welded to not less than 0.20 square inch (129
mm2) of bond beam reinforcement placed not less than 6 inches
(152 mm) from the top of the wall.
v Roofs must be anchored to bond beams and to the tops
of other walls. The material requirements for the bolts
are given in Section 2103.11.5.
2109.7.4 Walls adjoining structural framing. Where walls are
dependent upon the structural frame for lateral support, they
shall be anchored to the structural members with metal anchors
or otherwise keyed to the structural members. Metal anchors
shall consist of 1/2-inch (12.7 mm) bolts spaced at 48 inches
(1219 mm) o.c. embedded 4 inches (102 mm) into the masonry,
or their equivalent area.
v Selection of connectors for anchoring masonry to steel
beams and columns is based on the loads that must be
resisted. Lateral restraint perpendicular to the wall is required as a location of lateral support. Diaphragm transfer of shear forces is also required parallel to the wall, if
such forces occur. Alternative methods of reinforcement
can be used if the cross-sectional area and spacing are
equivalent.
2109.8 Adobe construction. Adobe construction shall comply
with this section and shall be subject to the requirements of this
code for Type V construction.
v Adobe masonry was popular in the southwest United
States due to the availability of soil for units, the limited
rainfall and low humidity to dry the units, the thermal
21-55
2109.8.1 – 2109.8.2.1.2
mass provided by the completed adobe structure and
the low cost of this form of construction. Requirements
for adobe construction are based on previous requirements in the SBC and the UBC. They are a combination
of empirical provisions and rudimentary engineering.
Since there are no ASTM standards for adobe materials, test methods have been included in the code. Design is based on gross cross-sectional dimensions.
Requirements for unstabilized adobe are contained in
Section 2109.8.1. Requirements for stabilized adobe are
contained in Section 2109.8.2. Requirements in Sections
2109.8.3 and 2109.8.4 apply to both unstabilized and stabilized adobe. This is one of the few sources for such design information.
2109.8.1 Unstabilized adobe.
v Unstabilized adobe does not contain stabilizers and is
generally not as durable or dimensionally stable as stabilized adobe.
2109.8.1.1 Compressive strength. Adobe units shall have an
average compressive strength of 300 psi (2068 kPa) when tested
in accordance with ASTM C 67. Five samples shall be tested
and no individual unit is permitted to have a compressive
strength of less than 250 psi (1724 kPa).
v Average compressive strength, based on five specimens tested in accordance with ASTM C 67, must be at
least 300 psi (2068 kPa).
2109.8.1.2 Modulus of rupture. Adobe units shall have an average modulus of rupture of 50 psi (345 kPa) when tested in accordance with the following procedure. Five samples shall be
tested and no individual unit shall have a modulus of rupture of
less than 35 psi (241 kPa).
v Average modulus of rupture, based on five specimens
tested in accordance with Sections 2109.8.1.2.1
through 2109.8.1.2.4, must be at least 50 psi (345 kPa).
2109.8.1.2.1 Support conditions. A cured unit shall be simply
supported by 2-inch-diameter (51 mm) cylindrical supports located 2 inches (51 mm) in from each end and extending the full
width of the unit.
v These required support conditions are typical for modulus of rupture tests.
2109.8.1.2.2 Loading conditions. A 2-inch-diameter (51 mm)
cylinder shall be placed at midspan parallel to the supports.
v Loading through a hydraulic cylinder at midspan is common for these tests.
2109.8.1.2.3 Testing procedure. A vertical load shall be applied to the cylinder at the rate of 500 pounds per minute (37
N/s) until failure occurs.
v The required application of vertical load is easily controlled in testing laboratories.
21-56
MASONRY
2109.8.1.2.4 Modulus of rupture determination. The modulus of rupture shall be determined by the equation:
fr = 3WLs /2bt 2
(Equation 21-4)
where, for the purposes of this section only:
b
= Width of the test specimen measured parallel to the
loading cylinder, inches (mm).
fr = Modulus of rupture, psi (MPa).
Ls = Distance between supports, inches (mm).
t
= Thickness of the test specimen measured parallel to the
direction of load, inches (mm).
W = The applied load at failure, pounds (N).
v Equation 21-4 is based on simple engineering mechanics and is valid for all rectangular specimens tested in
this fashion.
2109.8.1.3 Moisture content requirements. Adobe units shall
have a moisture content not exceeding 4 percent by weight.
v This section limits the moisture content of unstabilized
adobe units to acceptable levels.
2109.8.1.4 Shrinkage cracks. Adobe units shall not contain
more than three shrinkage cracks and any single shrinkage crack
shall not exceed 3 inches (76 mm) in length or 1/8 inch (3.2 mm)
in width.
v As adobe units dry, they shrink and can crack. This section places limits on those potential cracks to keep the masonry structurally sound and reasonably water resistant.
2109.8.2 Stabilized adobe.
v This type of adobe is manufactured with stabilizers to increase its durability and decrease its water absorption.
2109.8.2.1 Material requirements. Stabilized adobe shall
comply with the material requirements of unstabilized adobe in
addition to Sections 2109.8.2.1.1 and 2109.8.2.1.2.
v Stabilized adobe must comply with the few material requirements for unstabilized adobe in Section 2109.8.1.
Stabilized units must also comply with soil compatibility
and absorption requirements in Sections 2109.2.1.1
and 2109.2.1.2.
2109.8.2.1.1 Soil requirements. Soil used for stabilized adobe
units shall be chemically compatible with the stabilizing material.
v The soil and stabilizing materials must be chemically
compatible, so that the stabilized units will be durable.
2109.8.2.1.2 Absorption requirements. A 4-inch (102 mm)
cube, cut from a stabilized adobe unit dried to a constant weight
in a ventilated oven at 212°F to 239°F (100°C to 115°C), shall
not absorb more than 21/2- percent moisture by weight when
placed upon a constantly water-saturated, porous surface for
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2109.8.3 – 2109.8.4.3.2
seven days. A minimum of five specimens shall be tested and
each specimen shall be cut from a separate unit.
v This section prescribes a test method to verify that stabilized adobe units meet absorption limits.
2109.8.3 Working stress. The allowable compressive stress
based on gross cross-sectional area of adobe shall not exceed 30
psi (207 kPa).
v This section prescribes the allowable compressive
stress of adobe based on its gross cross-sectional area.
2109.8.3.1 Bolts. Bolt values shall not exceed those set forth in
Table 2109.8.3.1.
v This section requires the capacity of bolts to be based
on Table 2109.8.3.1. Specific types of bolts are not identified, but headed, bent-bar and plate anchors should all
be acceptable.
TABLE 2109.8.3.1
ALLOWABLE SHEAR ON BOLTS IN ADOBE MASONRY
DIAMETER OF BOLTS
(inches)
MINIMUM EMBEDMENT
(inches)
SHEAR
(pounds)
—
—
8
12
200
/4
15
300
18
400
1
21
500
11/8
24
600
1
/2
5/
3
7/
For SI:
8
1 inch = 25.4 mm, 1 pound = 4.448 N.
v The allowable shear values in this table are based on
the capacity of the adobe masonry. The capacity of the
anchor-bolt steel is much higher, so the lower strength
of the adobe controls.
v Because of the low strength of adobe masonry, it is limited to use in single-story buildings, unless a registered
design professional is hired, in which case two-story
buildings are permitted.
2109.8.4.1.2 Mortar restrictions. Mortar for stabilized adobe
units shall comply with Chapter 21 or adobe soil. Adobe soil
used as mortar shall comply with material requirements for stabilized adobe. Mortar for unstabilized adobe shall be portland
cement mortar.
v A variety of mortars are acceptable for stabilized adobe as
noted; however, portland cement-lime mortars are required for unstabilized adobe. Selection of a relatively
weak mortar that is compatible with the units is appropriate.
2109.8.4.1.3 Mortar joints. Adobe units shall be laid with full
head and bed joints and in full running bond.
v Full mortar joints, the same as for other solid units, are
required for adobe construction. Units are required to be
laid in running bond.
2109.8.4.1.4 Parapet walls. Parapet walls constructed of adobe
units shall be waterproofed.
v Waterproofing parapets reduce moisture infiltration into
the adobe.
2109.8.4.2 Wall thickness. The minimum thickness of exterior
walls in one-story buildings shall be 10 inches (254 mm). The
walls shall be laterally supported at intervals not exceeding 24
feet (7315 mm). The minimum thickness of interior load-bearing walls shall be 8 inches (203 mm). In no case shall the unsupported height of any wall constructed of adobe units exceed 10
times the thickness of such wall.
v Because of the low strength of adobe masonry walls,
thicker walls with more closely spaced supports are
required.
2109.8.4 Construction.
2109.8.4.3 Foundations.
v This section contains general construction requirements
for height restrictions, mortar restrictions, mortar joint construction and water-resistance requirements for parapet
walls and also specific requirements for wall thickness;
foundations; isolated piers and columns; tie beams; exterior finish and lintels.
v This section prescribes foundation requirements for
adobe masonry.
2109.8.4.1 General.
v This section contains general construction requirements
for height restrictions, mortar restrictions, mortar joint construction and water-resistance requirements for parapet
walls.
2109.8.4.1.1 Height restrictions. Adobe construction shall be
limited to buildings not exceeding one story, except that
two-story construction is allowed when designed by a registered
design professional.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2109.8.4.3.1 Foundation support. Walls and partitions constructed of adobe units shall be supported by foundations or
footings that extend not less than 6 inches (152 mm) above adjacent ground surfaces and are constructed of solid masonry (excluding adobe) or concrete. Footings and foundations shall
comply with Chapter 18.
v So that adobe masonry is properly supported, solid masonry or concrete foundations are required.
2109.8.4.3.2 Lower course requirements. Stabilized adobe
units shall be used in adobe walls for the first 4 inches (102 mm)
above the finished first-floor elevation.
v Because of their greater durability, stabilized adobe
units are required at the base of adobe walls. Conven21-57
2109.8.4.4 – 2110.1.1
tional masonry units can also be used to satisfy this
requirement.
2109.8.4.4 Isolated piers or columns. Adobe units shall not be
used for isolated piers or columns in a load-bearing capacity.
Walls less than 24 inches (610 mm) in length shall be considered
isolated piers or columns.
v Adobe units are not strong enough to carry significant
loads and are, therefore, not permitted to be used as
isolated piers or columns.
2109.8.4.5 Tie beams. Exterior walls and interior load-bearing
walls constructed of adobe units shall have a continuous tie
beam at the level of the floor or roof bearing and meeting the following requirements.
v To distribute loads more evenly into the adobe, tie
beams are required at the floor or roof levels. Tie beams
can be constructed of concrete or wood as described in
Sections 2109.8.4.5.1 and 2108.8.4.5.2, respectively.
2109.8.4.5.1 Concrete tie beams. Concrete tie beams shall be a
minimum depth of 6 inches (152 mm) and a minimum width of
10 inches (254 mm). Concrete tie beams shall be continuously
reinforced with a minimum of two No. 4 reinforcing bars. The
ultimate compressive strength of concrete shall be at least 2,500
psi (17.2 MPa) at 28 days.
v This section provides requirements for concrete tie beams
to be cast above adobe masonry walls to distribute loads
from floors and roofs.
2109.8.4.5.2 Wood tie beams. Wood tie beams shall be solid or
built up of lumber having a minimum nominal thickness of 1
inch (25 mm), and shall have a minimum depth of 6 inches (152
mm) and a minimum width of 10 inches (254 mm). Joints in
wood tie beams shall be spliced a minimum of 6 inches (152
mm). No splices shall be allowed within 12 inches (305 mm) of
an opening. Wood used in tie beams shall be approved naturally
decay-resistant or pressure-treated wood.
v This section provides requirements for wood tie beams
to be constructed above adobe masonry walls to distribute loads from floors and roofs.
2109.8.4.6 Exterior finish. Exterior walls constructed of
unstabilized adobe units shall have their exterior surface covered with a minimum of two coats of portland cement plaster
having a minimum thickness of 3/4 inch (19.1 mm) and conforming to ANSI A42.2. Lathing shall comply with ANSI A42.3.
Fasteners shall be spaced at 16 inches (406 mm) o.c. maximum.
Exposed wood surfaces shall be treated with an approved wood
preservative or other protective coating prior to lath application.
v Unstabilized adobe must be coated with plaster to increase its durability.
2109.8.4.7 Lintels. Lintels shall be considered structural members and shall be designed in accordance with the applicable
provisions of Chapter 16.
21-58
MASONRY
v Lintels over door and window openings are required to
be structurally designed to carry imposed loads and to
distribute those loads into the supporting adobe.
SECTION 2110
GLASS UNIT MASONRY
2110.1 Scope. This section covers the empirical requirements
for nonload-bearing glass unit masonry elements in exterior or
interior walls.
v Section 2110 contains provisions for glass unit masonry
walls, which are nearly identical to the glass unit masonry provisions in Chapter 7 of ACI 530/ASCE 5/TMS
402. Because those provisions are essentially the
same, IBC Section 2101.2.4 permits glass unit masonry
to comply with the provisions of Chapter 7 of ACI
530/ASCE 5/TMS 402 or of Section 2110.
Glass unit masonry panels are permitted to be used
in interior or exterior walls, provided that they are
nonload bearing and comply with the requirements of
Section 2110, which are partly empirical and partly
based on tests.
2110.1.1 Limitations. Solid or hollow approved glass block
shall not be used in fire walls, party walls, fire barriers or fire
partitions, or for load-bearing construction. Such blocks shall be
erected with mortar and reinforcement in metal channel-type
frames, structural frames, masonry or concrete recesses, embedded panel anchors as provided for both exterior and interior
walls or other approved joint materials. Wood strip framing shall
not be used in walls required to have a fire-resistance rating by
other provisions of this code.
Exceptions:
1. Glass-block assemblies having a fire protection rating
of not less than 3/4 hour shall be permitted as opening
protectives in accordance with Section 715 in fire barriers and fire partitions that have a required fire-resistance rating of 1 hour or less and do not enclose exit
stairways or exit passageways.
2. Glass-block assemblies as permitted in Section 404.5,
Exception 2.
v Structural glass blocks are not permitted in fire walls,
party walls, fire barrier walls or fire partitions, with two
exceptions. Exception 1 permits glass blocks that have
been tested and classified for a 3/4-hour fire protection
rating in openings to be used in fire barrier walls or fire
partitions with a required fire-resistance rating of 1 hour
or less. Since 1-hour fire barrier walls can be utilized to
enclose interior exit stairways and exit ramps (see Section 1019.1), as well as exit passageways (see Section
1020.3), the exception does not apply to those locations. This is consistent with Sections 1019.1.1 and
1020.4, which limit openings in these exit components
to those that are necessary for egress purposes. Exception 2 permits glass blocks to be installed in accordance
with the requirements in Section 404.5, Exception 2 for
the enclosure of atriums. Because Section 404.5 re2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2110.2 – 2110.3.2
quires a 1- hour fire barrier wall to enclose an atrium,
this exception is redundant since Exception 1 already
permits this.
and be capable of resisting horizontal forces. Panels exceeding these size limits require intermediate structural
supports so that loads can be adequately resisted.
2110.2 Units. Hollow or solid glass-block units shall be standard or thin units.
2110.3.1 Exterior standard-unit panels. The maximum area
of each individual exterior standard-unit panel shall be 144
square feet (13.4 m2) when the design wind pressure is 20 psf
(958 N/m2). The maximum panel dimension between structural
supports shall be 25 feet (7620 mm) in width or 20 feet (6096
mm) in height. The panel areas are permitted to be adjusted in
accordance with Figure 2110.3.1 for other wind pressures.
v This section contains minimum requirements for glass
masonry units, since a corresponding ASTM standard
does not exist. Units are permitted to be either hollow or
solid and are required to meet requirements for either
standard or thin units.
Glass units are usually factory coated at their edges.
Uncoated glass-block units can be field coated by following the manufacturer’s instructions.
2110.2.1 Standard units. The specified thickness of standard
units shall be 37/8 inches (98 mm).
v This section requires a specified thickness for standard
glass masonry units of 3 7/8 inches (98 mm).
2110.2.2 Thin units. The specified thickness of thin units shall
be 31/8 inches (79 mm) for hollow units or 3 inches (76 mm) for
solid units.
v Thicknesses for thin glass unit masonry are given in this
section.
2110.3 Panel size.
FIGURE 2110.3.1. See below.
v The wind load resistance curve represents capacities
for a variety of panel conditions. The 144-square-feet
(13 m2) area limit is based on a safety factor of 2.7 when
the design wind pressure is 20 psf (958 N/m2).
2110.3.2 Exterior thin-unit panels. The maximum area of each
individual exterior thin-unit panel shall be 85 square feet (7.9 m2).
The maximum dimension between structural supports shall be 15
feet (4572 mm) in width or 10 feet (3048 mm) in height. Thin
units shall not be used in applications where the design wind pressure exceeds 20 psf (958 N/m2).
DESIGN WIND PRESSURE, psf
v This section provides limits on the size of exterior standard-unit and thin-unit panels, interior panels, solid
glass-block panels and curved glass-block panels.
The glass-block panels must be restrained laterally
v Single panels of glass block are limited to a maximum
length of 25 feet (7620 mm) and a maximum height of
20 feet (6096 mm) between structural supports. When
subjected to a wind pressure of 20 psf (958 N/m2), any
single panel cannot exceed 144 square feet (13 m2) in
area. This maximum panel permissible area can be adjusted, however, for other wind pressures by the use of
Code Figure 2110.3.1.
AREA OF PANEL, sq. ft.
For SI:
1 square foot = 0.0929 m2, 1 pound per square foot = 47.9 N/m2.
FIGURE 2110.3.1
GLASS MASONRY DESIGN WIND LOAD RESISTANCE
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-59
2110.3.3 – 2110.5
v The limitations on the use of exterior panels with
thin-unit glass block are more restrictive than those in
Section 2110.3.1 for exterior panels with standard units,
since thin units are not as strong as standard ones.
2110.3.3 Interior panels. The maximum area of each individual standard-unit panel shall be 250 square feet (23.2 m2). The
maximum area of each thin-unit panel shall be 150 square feet
(13.9 m2). The maximum dimension between structural supports shall be 25 feet (7620 mm) in width or 20 feet (6096 mm)
in height.
v Interior panels can be larger than exterior ones since
wind pressures are expected to be lower.
2110.3.4 Solid units. The maximum area of solid glass-block
wall panels in both exterior and interior walls shall not be more
than 100 square feet (9.3 m2).
v Panels constructed of solid glass block must also meet
the requirements of this section.
2110.3.5 Curved panels. The width of curved panels shall conform to the requirements of Sections 2110.3.1, 2110.3.2 and
2110.3.3, except additional structural supports shall be provided
at locations where a curved section joins a straight section, and
at inflection points in multicurved walls.
v Curved panels of glass block must meet the appropriate
requirements of Sections 2110.3.1 through 2110.3.3,
plus the requirements for additional supports at critical
locations as defined in this section.
2110.4 Support.
v This section requires that glass-unit masonry panels be
laterally supported by panel anchors, channel-type restraints or a combination of both. Channel-type restraints can be made of concrete, masonry, metal, wood
or other materials, provided that adequate lateral support is achieved.
2110.4.1 Isolation. Glass unit masonry panels shall be isolated
so that in-plane loads are not imparted to the panel.
v Isolation joints are needed at the top and sides of
glass-unit masonry panels so that in-plane forces are
not transferred to the panels.
2110.4.2 Vertical. Maximum total deflection of structural members supporting glass unit masonry shall not exceed l/600.
v The sizes of structural members supporting glass-block
panels must be determined by structural analysis in order to avoid excessive deflections that could damage
the glass-block construction. Deflections of supporting
members are limited to a maximum of l/600, where l is
the span of the supporting member.
2110.4.3 Lateral. Glass unit masonry panels more than one unit
wide or one unit high shall be laterally supported along their
tops and sides. Lateral support shall be provided by panel anchors along the top and sides spaced not more than 16 inches
21-60
MASONRY
(406 mm) o.c. or by channel-type restraints. Glass unit masonry
panels shall be recessed at least 1 inch (25 mm) within channels
and chases. Channel-type restraints shall be oversized to accommodate expansion material in the opening and packing and sealant between the framing restraints and the glass unit masonry
perimeter units. Lateral supports for glass unit masonry panels
shall be designed to resist applied loads, or a minimum of 200
pounds per lineal feet (plf) (2919 N/m) of panel, whichever is
greater.
Exceptions:
1. Lateral support at the top of glass unit masonry panels
that are no more than one unit wide shall not be
required.
2. Lateral support at the sides of glass unit masonry panels that are no more than one unit high shall not be
required.
v Glass-block panels in exterior masonry walls or in openings of structural framing systems (curtain walls) are required to be restrained laterally to resist both external and
internal pressures caused by wind and horizontal forces
from earthquakes. Lateral support can be provided by
channel-type or panel anchors.
Adhering to the dimensional limitations imposed on
glass-block panels and complying with the requirements
for construction will generally produce glass-block elements that adequately resist normal wind conditions. In regions with very high winds or high seismic risk, however,
glass-block panels and their anchorage to supporting
structural elements should be checked for adequacy.
The exceptions in this section recognize that loads and
expected movement of small glass-unit panels are small
enough to permit installation without isolation joints.
2110.4.3.1 Single unit panels. Single unit glass unit masonry
panels shall conform to the requirements of Section 2110.4.3,
except lateral support shall not be provided by panel anchors.
v Single-unit panels generally have the same requirements as multiple-unit panels described in Section
2110.4.3.
2110.5 Expansion joints. Glass unit masonry panels shall be
provided with expansion joints along the top and sides at all
structural supports. Expansion joints shall have sufficient thickness to accommodate displacements of the supporting structure,
but shall not be less than 3/8 inch (9.5 mm) in thickness. Expansion joints shall be entirely free of mortar or other debris and
shall be filled with resilient material. The sills of glass-block
panels shall be coated with approved water-based asphaltic
emulsion, or other elastic waterproofing material, prior to laying
the first mortar course.
v Sills supporting glass-block panel on a mortar bed are
required to be first made water resistant with a heavy
coat of asphalt emulsion or other approved water-resistant material. When the emulsion on the sill has dried,
the full mortar bed can be placed, followed by the lowest
course of glass block.
Before any glass-block units are placed, however, the
head and jamb areas over the full height and width of
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2110.6 – 2111.3.1
the glass-block panel should be provided with expansion strips [3/8 inches (9.5 mm) thick] made for this purpose.
Glass-block units should be placed in successive
courses on mortar beds containing panel reinforcement
as required by the project documents, either directly or
through reference to the manufacturer’s instructions.
Panel reinforcement should not be placed across expansion joints. Joints should be tooled smooth and concave before the mortar sets and joints around the perimeter of the panel should be raked out sufficiently to
receive filler and caulking materials.
After the mortar sets, expansion joints are typically
closed with a sealant.
2110.6 Mortar. Mortar for glass unit masonry shall comply
with Section 2103.7.
v See the commentary to Section 2103.7. Glass-unit masonry panels are to be laid in Type N or S mortar.
2110.7 Reinforcement. Glass unit masonry panels shall have
horizontal joint reinforcement spaced not more than 16 inches
(406 mm) on center, located in the mortar bed joint, and extending the entire length of the panel but not across expansion joints.
Longitudinal wires shall be lapped a minimum of 6 inches (152
mm) at splices. Joint reinforcement shall be placed in the bed
joint immediately below and above openings in the panel. The
reinforcement shall have not less than two parallel longitudinal
wires of size W1.7 (MW11), and have welded cross wires of
size W1.7 (MW11).
v Panel reinforcement made especially for glass block is
typically of the ladder type, formed of two W1.7 galvanized wires spaced 2 inches (51 mm) apart with W1.7
galvanized cross wires welded at 16-inch (406 mm) intervals. Where placed continuously, the sections are required to lap at least 6 inches (152 mm). Such reinforcement must not extend across expansion joints because
it would compromise their effectiveness.
SECTION 2111
MASONRY FIREPLACES
2111.1 Definition. A masonry fireplace is a fireplace constructed of concrete or masonry. Masonry fireplaces shall be
constructed in accordance with this section, Table 2111.1 and
Figure 2111.1.
v The provisions of this section apply to the design and installation of concrete and masonry fireplaces, which for
simplicity are referred to as “masonry fireplaces.”
TABLE 2111.1. See page 21-62.
v This table summarizes many of the requirements for
fireplaces contained in Section 2111. Commentary to
the listed section references should be reviewed for information on each item in the table.
This table does not address all the requirements of
Section 2111. Each code section must be checked to
see that a fireplace is in compliance.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
FIGURE 2111.1. See page 21-63.
v This figure graphically shows many of the requirements
for fireplaces contained in Section 2111. This figure
does not address all the requirements of Section 2111.
2111.2 Footings and foundations. Footings for masonry fireplaces and their chimneys shall be constructed of concrete or
solid masonry at least 12 inches (305 mm) thick and shall extend
at least 6 inches (153 mm) beyond the face of the fireplace or
foundation wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be at least 12 inches
(305 mm) below finished grade.
v Masonry fireplaces and chimneys must be supported
on adequate footings due to their weight and the forces
imposed on them by wind, earthquakes and other effects. This section prescribes minimum footing requirements that are typically adequate for standard fireplaces and chimneys. Extremely large, tall or heavy
fireplaces and chimneys, however, may need more substantial foundations (see Item T in Figure 2111.1).
2111.2.1 Ash dump cleanout. Cleanout openings, located
within foundation walls below fireboxes, when provided, shall
be equipped with ferrous metal or masonry doors and frames
constructed to remain tightly closed, except when in use.
Cleanouts shall be accessible and located so that ash removal
will not create a hazard to combustible materials.
v Noncombustible, tightly sealed cleanout doors are required to reduce the danger of fire spread through the
cleanout openings. Cleanout openings are required to
be easily accessible to allow ash to be readily removed.
2111.3 Seismic reinforcing. Masonry or concrete fireplaces
shall be constructed, anchored, supported and reinforced as required in this chapter. In Seismic Design Category D, masonry
and concrete fireplaces shall be reinforced and anchored as detailed in Sections 2111.3.1, 2111.3.2, 2111.4 and 2111.4.1 for
chimneys serving fireplaces. In Seismic Design Category A, B
or C, reinforcement and seismic anchorage is not required. In
Seismic Design Category E or F, masonry and concrete chimneys shall be reinforced in accordance with the requirements of
Sections 2101 through 2109.
v Unreinforced fireplaces and chimneys subjected to
strong ground motion have sustained damage in past
earthquakes. The requirements in this section provide
minimum reinforcement in an effort to increase structural integrity during such events. More substantial reinforcement may, however, be required in areas of high
seismicity or for atypical fireplaces and chimneys.
2111.3.1 Vertical reinforcing. For fireplaces with chimneys up
to 40 inches (1016 mm) wide, four No. 4 continuous vertical
bars, anchored in the foundation, shall be placed in the concrete,
between wythes of solid masonry or within the cells of hollow
unit masonry and grouted in accordance with Section 2103.10.
For fireplaces with chimneys greater than 40 inches (1016 mm)
wide, two additional No. 4 vertical bars shall be provided for
21-61
TABLE 2111.1
MASONRY
TABLE 2111.1
SUMMARY OF REQUIREMENTS FOR MASONRY FIREPLACES AND CHIMNEYSa
ITEM
Hearth and hearth extension thickness
LETTER
REQUIREMENTS
SECTION
A
4-inch minimum thickness for hearth, 2-inch minimum thickness for
hearth extension.
2111.9
B
8 inches for fireplace opening less than 6 square feet. 12 inches for
fireplace opening greater than or equal to 6 square feet.
2111.10
C
16 inches for fireplace opening less than 6 square feet. 20 inches for
fireplace opening greater than or equal to 6 square feet.
2111.10
—
20-inch minimum firebox depth. 12-inch minimum firebox depth for
Rumford fireplaces.
2111.6
Hearth and hearth extension reinforcing
D
Reinforced to carry its own weight and all imposed loads.
2111.9
Thickness of wall of firebox
E
10 inches solid masonry or 8 inches where firebrick lining is used.
2111.5
Hearth extension (each side of opening)
Hearth extension (front of opening)
Firebox dimensions
Distance from top of opening to throat
Smoke chamber wall thickness
dimensions
F
Fireplace lintel
Chimney walls with flue lining
2111.7
2111.7.1
G
6 inches lined; 8 inches unlined. Not taller than opening width; walls not
inclined more than 45 degrees from vertical for prefabricated smoke
chamber linings or 30 degrees from vertical for corbeled masonry.
2111.8
H
Four No. 4 full-length bars for chimney up to 40 inches wide. Add two
No. 4 bars for each additional 40 inches or fraction of width, or for each
additional flue.
2111.3.1,
2113.3.1
Chimney vertical reinforcing
Chimney horizontal reinforcing
8 inches minimum.
1
J
/4-inch ties at each 18 inches, and two ties at each bend in vertical steel.
2111.3.2,
2113.3.2
L
Noncombustible material with 4-inch bearing length of each side of
opening.
2111.7
M
4-inch-thick solid masonry with 5/8-inch fireclay liner or equivalent.
1/ -inch grout or airspace between fireclay liner and wall.
2
2113.11.1
Effective flue area (based on area of
fireplace opening and chimney)
P
Clearances
From chimney
From fireplace
From combustible trim or materials
Above roof
R
See Section 2113.16.
2113.16
2 inches interior, 1 inch exterior or 12 inches from lining.
2 inches back or sides or 12 inches from lining.
6 inches from opening
3 feet above roof penetration, 2 feet above part of structure within 10 feet.
2113.19
2111.11
2111.12
2113.9
3
Anchorage strap
Number required
Embedment into chimney
Fasten to
Number of bolts
S
Footing
Thickness
Width
T
/16 inch by 1 inch
Two
12 inches hooked around outer bar with 6-inch extension.
4 joists
Two 1/2-inch diameter.
12-inch minimum.
6 inches each side of fireplace wall.
2111.4
2113.4.1
2111.2
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 square foot = 0.0929 m2, 1 degree = 0.017 rad.
a. This table provides a summary of major requirements for the construction of masonry chimneys and fireplaces. Letter references are to Figure 2111.1, which shows
examples of typical construction. This table does not cover all requirements, nor does it cover all aspects of the indicated requirements. For the actual mandatory requirements of the code, see the indicated section of text.
21-62
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
For SI:
FIGURE 2111.1
1 inch = 25.4 mm, 1 foot = 304.8 mm.
FIGURE 2111.1
FIREPLACE AND CHIMNEY DETAILS
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-63
2111.3.2 – 2111.6
MASONRY
each additional 40 inches (1016 mm) in width or fraction
thereof.
and shall be laid with medium-duty refractory mortar conforming to ASTM C 199.
v These requirements are traditional minimum prescriptive provisions to help maintain the integrity of fireplaces
and chimneys during earthquakes. To resist strong
earthquakes, however, more substantial reinforcement
may be required (see Item H in Figure 2111.1).
v This section specifies the minimum thicknesses of refractory brick or solid masonry necessary to contain the generated heat.
Solid masonry walls forming the firebox are required to
have a minimum total thickness of 8 inches (204 mm), including the refractory lining.
The refractory lining is to consist of a low-duty, fire-clay
refractory brick with a minimum thickness of 2 inches (52
mm), laid with medium-duty refractory mortar. Mortar
joints are generally 1/16 to 3/16 inch (1.6 to 4.8 mm) thick,
but not thicker than 1/4 inch (6.4 mm), to reduce thermal
movements and prevent joint deterioration.
Where a firebrick lining is not used in firebox construction, the wall thickness is not to be less than 10
inches (254 mm) of solid masonry. Firebrick is required
to conform to ASTM C 27 or ASTM C 1261. Firebrick
must be laid with medium-duty refractory mortar conforming to ASTM C 199 (see Item E in Figure 2111.1).
2111.3.2 Horizontal reinforcing. Vertical reinforcement shall
be placed enclosed within 1/4-inch (6.4 mm) ties or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete; or placed in the
bed joints of unit masonry at a minimum of every 18 inches (457
mm) of vertical height. Two such ties shall be provided at each
bend in the vertical bars.
v These requirements are traditional minimum prescriptive provisions to help maintain the integrity of fireplaces
and chimneys during earthquakes. The vertical reinforcement required by Section 2111.3.1 must be enclosed within the horizontal reinforcement required by
this section. To resist strong earthquakes, however,
more substantial reinforcement may be required (see
Item J in Figure 2111.1).
2111.4 Seismic anchorage. Masonry and concrete chimneys in
Seismic Design Category D shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade, except
where constructed completely within the exterior walls. Anchorage shall conform to the following requirements.
v Fireplaces and chimneys can fail by overturning during
earthquakes. Seismic anchorage to floors and roof diaphragms is required to reduce the cantilevered height of
the chimney and thereby help prevent overturning (see
Item S in Figure 2111.1).
2111.4.1 Anchorage. Two 3/16-inch by 1-inch (4.8 mm by 25.4
mm) straps shall be embedded a minimum of 12 inches (305
mm) into the chimney. Straps shall be hooked around the outer
bars and extend 6 inches (152 mm) beyond the bend. Each strap
shall be fastened to a minimum of four floor joists with two
1/ -inch (12.7 mm) bolts.
2
v The prescriptive requirements in this section are traditional for typical fireplaces and chimneys. More substantial anchorage may be required in areas of high
seismicity, for large fireplaces or where the distance between floor and roof diaphragms is large.
2111.5 Firebox walls. Masonry fireboxes shall be constructed
of solid masonry units, hollow masonry units grouted solid,
stone or concrete. When a lining of firebrick at least 2 inches (51
mm) in thickness or other approved lining is provided, the minimum thickness of back and sidewalls shall each be 8 inches (203
mm) of solid masonry, including the lining. The width of joints
between firebricks shall not be greater than 1/4 inch (6.4 mm).
When no lining is provided, the total minimum thickness of
back and sidewalls shall be 10 inches (254 mm) of solid masonry. Firebrick shall conform to ASTM C 27 or ASTM C 1261
21-64
2111.5.1 Steel fireplace units. Steel fireplace units are permitted to be installed with solid masonry to form a masonry fireplace provided they are installed according to either the
requirements of their listing or the requirements of this section.
Steel fireplace units incorporating a steel firebox lining shall be
constructed with steel not less than 1/4 inch (6.4 mm) in thickness, and an air-circulating chamber which is ducted to the interior of the building. The firebox lining shall be encased with
solid masonry to provide a total thickness at the back and sides
of not less than 8 inches (203 mm), of which not less than 4
inches (102 mm) shall be of solid masonry or concrete. Circulating air ducts employed with steel fireplace units shall be constructed of metal or masonry.
v This section provides minimum requirements for steel linings used in masonry fireplaces to improve heat flow.
2111.6 Firebox dimensions. The firebox of a concrete or masonry fireplace shall have a minimum depth of 20 inches (508
mm). The throat shall not be less than 8 inches (203 mm) above
the fireplace opening. The throat opening shall not be less than 4
inches (102 mm) in depth. The cross-sectional area of the passageway above the firebox, including the throat, damper and
smoke chamber, shall not be less than the cross-sectional area of
the flue.
Exception: Rumford fireplaces shall be permitted provided
that the depth of the fireplace is at least 12 inches (305 mm)
and at least one-third of the width of the fireplace opening,
and the throat is at least 12 inches (305 mm) above the lintel,
and at least 1/20 the cross-sectional area of the fireplace opening.
v The proper functioning of the fireplace depends on the
size of the face opening and the chimney dimensions,
which in turn are related to the room size [see Figure
2111.6(1)]. This section specifies a minimum depth of
20 inches (508 mm) for the combustion chamber because that depth influences the draft requirement. The
dimensions of the firebox (depth, opening size and
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2111.7 – 2111.7.1
shape) are usually based on two considerations: aesthetics and the need to prevent the room from overheating. Suggested dimensions for single-opening fireboxes
are given in technical publications of the Brick Institute
of America (BIA) and the National Concrete Masonry
Association (NCMA).
This section also provides additional criteria for the
throat’s location and minimum cross-sectional area.
Those criteria are based on many years of construction
of successfully functioning fireplaces.
The exception permits the use of Rumford fireplaces
and the dimensions associated with this design style.
Rumford fireplaces are tall, shallow fireplaces that can
radiate a large amount of heat into a room.
The code reference to the depth of the fireplace is interpreted as the depth of the firebox [see Figure
2111.6(2)]. The throat is required to be made at least 12
inches (305 mm) above the lintel and at least one-twentieth of the cross-sectional area of the fireplace opening.
Smoke chambers and flues for Rumford fireplaces
should be sized and built like other masonry fireplaces.
While those who build Rumford fireplaces do not totally
agree about how they work, many books and guides address their construction.
2111.7 Lintel and throat. Masonry over a fireplace opening
shall be supported by a lintel of noncombustible material. The
minimum required bearing length on each end of the fireplace
opening shall be 4 inches (102 mm). The fireplace throat or
damper shall be located a minimum of 8 inches (203 mm) above
the top of the fireplace opening.
v Permanent support for the masonry above the fireplace
opening is provided by noncombustible lintels of steel,
masonry or concrete (see Item L of Figure 2111.1). Combustible lintels (for example, those made from wood) are
not appropriate due to the risk of fire damage and the
probable collapse of the masonry above the opening.
The minimum bearing requirement of 4 inches (102
mm) is empirical, based on typical masonry fireplace
openings. Lintels that support more than the typical weight
of masonry above the fireplace opening may require a
larger bearing area.
The throat of a fireplace is the slot-like opening above
the firebox, through which flames, smoke and hot combustion gases pass into the smoke chamber. The throat is
as wide as the combustion chamber and is required to be
located at least 8 inches (204 mm) above the lintel for conventional fireplaces. The back wall of the combustion
chamber extends up to the throat, which is provided with a
metal damper.
2111.7.1 Damper. Masonry fireplaces shall be equipped with a
ferrous metal damper located at least 8 inches (203 mm) above
12" MIN.
MANTEL
DAMPER
OPENING
FIREBOX
SMOKE SHELF
LINTEL
THROAT
20" MIN*
A
FIREBOX OR
COMBUSTION CHAMBER
A (SEE FIGURE 2110.10 FOR
PLAN VIEW)
HEARTH
BASE ASSEMBLY
THROAT
MIN. 5% (1/20th)
CROSSSECTIONAL
AREA OF
FIREPLACE
OPENING
MASONRY
8" MIN
CHAMBER
SMOKE
CHIMNEY
FLUE LINER
WOOD
FLOOR
HEARTH EXTENSION
FOUNDATION WALLS,
MASONRY OR CONCRETE
12" MIN.
(MIN. 1/3 WIDTH OF
FIREPLACE OPENING)
FIREPLACE
OPENING
HEARTH
CONCRETE FOOTING
*EXCEPT AS PERMITTED FOR RUMFORD FIREPLACES [SEE FIGURE 2111.11(2)]
For SI:
1 inch = 25.4 mm.
Figure 2111.6(1)
SECTION THROUGH FIREPLACE
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
For SI:
1 inch = 25.4 mm.
Figure 2111.6(2)
RUMFORD FIREPLACE
21-65
2111.8 – 2111.11
the top of the fireplace opening. Dampers shall be installed in
the fireplace or at the top of the flue venting the fireplace, and
shall be operable from the room containing the fireplace.
Damper controls shall be permitted to be located in the fireplace.
v A damper is used to close the chimney flue when the
fireplace is not in use. This section provides guidance
on its location and construction.
2111.8 Smoke chamber walls. Smoke chamber walls shall be
constructed of solid masonry units, hollow masonry units
grouted solid, stone or concrete. Corbeling of masonry units
shall not leave unit cores exposed to the inside of the smoke
chamber. The inside surface of corbeled masonry shall be
parged smooth. Where no lining is provided, the total minimum
thickness of front, back and sidewalls shall be 8 inches (203
mm) of solid masonry. When a lining of firebrick at least 2
inches (51 mm) thick, or a lining of vitrified clay at least 5/8 inch
(15.9 mm) thick, is provided, the total minimum thickness of
front, back and sidewalls shall be 6 inches (152 mm) of solid
masonry, including the lining. Firebrick shall conform to ASTM
C 27 or ASTM C 1261 and shall be laid with refractory mortar
conforming to ASTM C 199.
v The minimum wall thickness specified for the throat and
smoke chamber is required to provide support for the flue
construction, as well as adequate thermal insulation for
the adjacent combustible construction.
In conventional fireplace construction, the smoke
chamber is a tapering section whose vertical dimension is
measured from the damper or throat to the bottom of the
chimney flue. The actual height is a function of the fireplace opening.
2111.8.1 Smoke chamber dimensions. The inside height of the
smoke chamber from the fireplace throat to the beginning of the
flue shall not be greater than the inside width of the fireplace
opening. The inside surface of the smoke chamber shall not be
inclined more than 45 degrees (0.76 rad) from vertical when prefabricated smoke chamber linings are used or when the smoke
chamber walls are rolled or sloped rather than corbeled. When
the inside surface of the smoke chamber is formed by corbeled
masonry, the walls shall not be corbeled more than 30 degrees
(0.52 rad) from vertical.
v This section specifies the smoke chamber configuration
that is needed for the proper function of the masonry chimney. Also see Table 2111.1, Item G, for smoke chamber
requirements.
2111.9 Hearth and hearth extension. Masonry fireplace
hearths and hearth extensions shall be constructed of concrete or
masonry, supported by noncombustible materials, and reinforced to carry their own weight and all imposed loads. No combustible material shall remain against the underside of hearths or
hearth extensions after construction.
v The fireplace hearth consists of two parts. The hearth,
commonly called the “inner hearth,” is the floor of the combustion chamber and is obviously constructed of
noncombustible material. The outer hearth, commonly
known as the “hearth extension,” projects beyond the face
21-66
MASONRY
of the fireplace into the room and also consists of
noncombustible materials, such as brick or concrete masonry, concrete, floor tile or stone (see Figure 2111.1,
Items A and D). The hearth extension may continue out
from the inner hearth at the same level or be stepped
down to a lower level. Minimum dimensions for the hearth
extension are prescribed in Section 2111.10 and are discussed in the commentary to that section.
Combustible forms and centers could ignite from exposure to heat from the adjacent fireplace and from burning
embers that escape the firebox; these and other similar
concealed, combustible components must be removed.
2111.9.1 Hearth thickness. The minimum thickness of fireplace hearths shall be 4 inches (102 mm).
v The required minimum thickness of 4 inches (102 mm) is
an empirical requirement that has historically been successful.
2111.9.2 Hearth extension thickness. The minimum thickness
of hearth extensions shall be 2 inches (51 mm).
Exception: When the bottom of the firebox opening is raised
at least 8 inches (203 mm) above the top of the hearth extension, a hearth extension of not less than 3/8-inch-thick (9.5
mm) brick, concrete, stone, tile or other approved
noncombustible material is permitted.
v These requirements are empirical and have historically
been successful.
2111.10 Hearth extension dimensions. Hearth extensions shall
extend at least 16 inches (406 mm) in front of, and at least 8
inches (203 mm) beyond, each side of the fireplace opening.
Where the fireplace opening is 6 square feet (0.557 m2) or larger,
the hearth extension shall extend at least 20 inches (508 mm) in
front of, and at least 12 inches (305 mm) beyond, each side of
the fireplace opening.
v The hearth extension is required to extend the full width of
the fireplace opening and at least 8 inches (203 mm) beyond each side of the opening. It is also required to extend
at least 16 inches (406 mm) out from the face of the fireplace. For fireplace openings larger than 6 square feet
(0.557 m2) in area, the hearth extension is required to
extend at least 20 inches (508 mm) beyond the face of
the fireplace and at least 12 inches (305 mm) beyond
each side of the fireplace opening (see Figure 2111.10).
The hearth extension is intended to serve as a
fire-protective separation between the firebox and adjacent combustible flooring or furnishings and to prevent
accidental spills of hot embers or logs from the fire.
2111.11 Fireplace clearance. Any portion of a masonry fireplace located in the interior of a building or within the exterior
wall of a building shall have a clearance to combustibles of not
less than 2 inches (51 mm) from the front faces and sides of masonry fireplaces and not less than 4 inches (102 mm) from the
back faces of masonry fireplaces. The airspace shall not be
filled, except to provide fireblocking in accordance with Section
2111.13.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2111.12 – 2111.14
Exceptions:
1. Masonry fireplaces listed and labeled for use in contact
with combustibles in accordance with UL 127, and installed in accordance with the manufacturer’s installation instructions, are permitted to have combustible
material in contact with their exterior surfaces.
v This figure clarifies Exception 3 to the clearance requirement for masonry fireplaces. The edge abutment
of combustible sheathing materials where there is an
adequate thickness of masonry is a long-standing practice that is considered safe, provided the minimum
clearance to the firebox lining is maintained.
2. When masonry fireplaces are constructed as part of
masonry or concrete walls, combustible materials shall
not be in contact with the masonry or concrete walls
less than 12 inches (306 mm) from the inside surface of
the nearest firebox lining.
2111.12 Mantel and trim. Woodwork or other combustible materials shall not be placed within 6 inches (152 mm) of a fireplace opening. Combustible material within 12 inches (305 mm)
of the fireplace opening shall not project more than 1/8 inch (3.2
mm) for each 1-inch (25 mm) distance from such opening.
3. Exposed combustible trim and the edges of sheathing
materials, such as wood siding, flooring and drywall,
are permitted to abut the masonry fireplace sidewalls
and hearth extension, in accordance with Figure
2111.11, provided such combustible trim or sheathing
is a minimum of 12 inches (306 mm) from the inside
surface of the nearest firebox lining.
v Combustible materials attached to the fireplace face,
such as wood trim and mantels, are not permitted to be
installed closer than 6 inches (152 mm) from the fireplace opening. Materials located above the opening
and that project excessively create a severe fire hazard,
however, and are required to have a minimum clearance of 12 inches (305 mm) from the fireplace opening.
4. Exposed combustible mantels or trim is permitted to be
placed directly on the masonry fireplace front surrounding the fireplace opening provided such combustible materials shall not be placed within 6 inches (153
mm) of a fireplace opening. Combustible material
within 12 inches (306 mm) of the fireplace opening
shall not project more than 1/8 inch (3.2 mm) for each
1-inch (25 mm) distance from such opening.
2111.13 Fireplace fireblocking. All spaces between fireplaces
and floors and ceilings through which fireplaces pass shall be
fireblocked with noncombustible material securely fastened in
place. The fireblocking of spaces between wood joists, beams or
headers shall be to a depth of 1 inch (25 mm) and shall only be
placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.
v Combustible materials, such as framing studs and
joists, must not be installed closer than 2 inches (51
mm) to the exterior surface of fireplace walls because of
the fire hazard to materials in this location. Heat transmitted through fireplace walls can ignite combustible
structural materials in contact with the walls. For this
reason, a minimum required clearance has been established from the fireplace to combustibles.
v Fireblocking is required to prevent the travel of flames,
smoke or hot gases to other areas of the building through
gaps between the chimney and the floor or ceiling assemblies. The 1-inch (25 mm) depth requirement is intended
to be both a minimum and a maximum.
2111.14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply
to ensure proper fuel combustion unless the room is mechaniMASONRY
20" MIN. FOR FIREPLACE
OPENINGS 6 SQ.FT.
AND LARGER
12" MIN. FOR FIREPLACE
OPENINGS 6 SQ.FT.
AND LARGER
16" MIN. FOR LESS THAN
6 SQ.FT. FIREPLACE
OPENING
FIREPLACE
OPENING
For SI:
HEARTH
8" MIN. FOR LESS THAN
6 SQ.FT. FIREPLACE
OPENING
PLAN VIEW
1 inch = 25.4 mm,
1 square foot = .0929 m2.
Figure 2111.10
HEARTH EXTENSION
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-67
2111.14.1 – 2112.1
MASONRY
Air intakes should be covered with screens to prevent
pests from entering the building when the fireplace is
not functioning.
2111.14.4 Clearance. Unlisted combustion air ducts shall be installed with a minimum 1-inch (25 mm) clearance to combustibles for all parts of the duct within 5 feet (1524 mm) of the duct
outlet.
v The 1-inch (25 mm) clearance is required to reduce the
risk of fire through the air intakes.
For SI: 1 inch = 25.4 mm
FIGURE 2111.11
ILLUSTRATION OF EXCEPTION TO
FIREPLACE CLEARANCE PROVISION
cally ventilated and controlled so that the indoor pressure is neutral or positive.
v Adequate airflow is needed to provide exterior oxygen
for the fire and to maintain draft through the chimney so
that toxic combustion gases can be exhausted. Adequate airflow is especially important in modern, tightly
sealed buildings.
2111.14.1 Factory-built fireplaces. Exterior combustion air
ducts for factory-built fireplaces shall be listed components of
the fireplace, and installed according to the fireplace manufacturer’s instructions.
v Factory-built fireplaces are required to include exterior
combustion air ducts. To function properly, these units
need to be installed according to the manufacturer’s
recommendations.
2111.14.2 Masonry fireplaces. Listed combustion air ducts for
masonry fireplaces shall be installed according to the terms of
their listing and manufacturer’s instructions.
v For proper functioning and airflow, air ducts for masonry
fireplaces must be installed according to the manufacturer’s recommendations (see also commentary, Section 2111.14).
2111.14.3 Exterior air intake. The exterior air intake shall be
capable of providing all combustion air from the exterior of the
dwelling. The exterior air intake shall not be located within the
garage, attic, basement or crawl space of the dwelling nor shall
the air intake be located at an elevation higher than the firebox.
The exterior air intake shall be covered with a corrosion-resistant screen of 1/4-inch (6.4 mm) mesh.
v Air intakes are required to provide air from outside of the
building. The air intakes are not permitted to be placed
in garages, basements, crawl spaces or other areas
where gases from the exhaust of automobiles, furnaces
and other sources could be brought into the building.
21-68
2111.14.5 Passageway. The combustion air passageway shall
be a minimum of 6 square inches (3870 mm2) and not more than
55 square inches (0.035 m2), except that combustion air systems
for listed fireplaces or for fireplaces tested for emissions shall be
constructed according to the fireplace manufacturer’s instructions.
v These minimum requirements are intended to provide
adequate airflow through the fireplace.
2111.14.6 Outlet. The exterior air outlet is permitted to be located in the back or sides of the firebox chamber or within 24
inches (610 mm) of the firebox opening on or near the floor. The
outlet shall be closable and designed to prevent burning material
from dropping into concealed combustible spaces.
v The requirements on the location of the outlet in the firebox chamber are needed for adequate airflow to the fire
while avoiding the direct flow of air into the adjacent
room. Such openings must not become clogged with
ash, which would restrict airflow. Even more important,
burning material must not drop into concealed combustible spaces due to the risk of fire damage to the building. Outlets must therefore be both closable and adequately designed to prevent this.
SECTION 2112
MASONRY HEATERS
2112.1 Definition. A masonry heater is a heating appliance constructed of concrete or solid masonry, hereinafter referred to as
“masonry,” having a mass of at least 1,760 pounds (800 kg), excluding the chimney and foundation, which is designed to absorb and store heat from a solid fuel fire built in the firebox by
routing the exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox includes
at least one 180-degree (3.14 rad) change in flow direction before entering the chimney, and that delivers heat by radiation
from the masonry surface of the heater that shall not exceed
230°F (110°C) except within 8 inches (203 mm) surrounding
the fuel loading door(s).
v Masonry heaters are appliances designed to absorb
and store heat from a relatively small fire and to radiate
that heat into the building interior. They are thermally
more efficient than traditional fireplaces because of their
design. Interior passageways through the heater allow
hot exhaust gases from the fire to transfer heat into the
masonry, which then radiates into the building.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2112.2 – 2113.3.1
2112.2 Installation. Masonry heaters shall be listed or installed
in accordance with ASTM E 1602.
v ASTM E 1602 provides guidelines for installing masonry heaters.
2112.3 Seismic reinforcing. Seismic reinforcing shall not be required within the body of a masonry heater whose height is
equal to or less than 2.5 times its body width and where the masonry chimney serving the heater is not supported by the body of
the heater. Where the masonry chimney shares a common wall
with the facing of the masonry heater, the chimney portion of the
structure shall be reinforced in accordance with Sections 2113
and 2113.4.
v Because of the large bulk and squat geometry of these
heaters, seismic reinforcement is not typically required.
Flexural tensile stresses, which typically cause damage
to unreinforced masonry, rarely occur. Where chimneys
extend above these heaters, however, seismic reinforcement is required by Section 2113. See the commentary to that section for additional information on this
requirement.
2112.4 Masonry heater clearance. Wood or other combustible
framing shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater, provided the wall thickness of
the firebox is not less than 8 inches (203 mm) and the wall thickness of the heat exchange channels is not less than 5 inches (127
mm). A clearance of at least 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a
combustible ceiling. The required space between the heater and
combustible material shall be fully vented to permit the free
flow of air around all heater surfaces.
v Heat conducted through masonry heater walls can ignite
combustible structural materials in contact with these
walls. For this reason, a minimum required clearance to
combustibles from masonry heaters has been established. Because masonry heaters typically generate more
heat for a longer period of time than traditional fireplaces,
greater clearances to combustible materials are needed
to reduce the risk of fire.
SECTION 2113
MASONRY CHIMNEYS
2113.1 General. A masonry chimney is a chimney constructed
of concrete or masonry, hereinafter referred to as “masonry.”
Masonry chimneys shall be constructed, anchored, supported
and reinforced as required in this chapter.
v A masonry chimney is a field-constructed assembly that
can consist of masonry units, grout, reinforced concrete,
rubble stone, fire-clay liners and mortars. A masonry
chimney is permitted to serve residential (low-heat), medium- and high-heat appliances. This section outlines the
general code requirements regarding construction details
for all masonry chimneys, including those serving masonry fireplaces regulated by Section 2111.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2113.2 Footings and foundations. Foundations for masonry
chimneys shall be constructed of concrete or solid masonry at
least 12 inches (305 mm) thick and shall extend at least 6 inches
(152 mm) beyond the face of the foundation or support wall on
all sides. Footings shall be founded on natural undisturbed earth
or engineered fill below frost depth. In areas not subjected to
freezing, footings shall be at least 12 inches (305 mm) below
finished grade.
v Masonry fireplaces and chimneys must be supported
on adequate foundations due to their weight and the
forces imposed on them by wind, earthquakes and
other effects. This section prescribes minimum foundation requirements that are typically adequate for standard chimneys.
Extremely large, tall or heavy chimneys, however, may
need more substantial foundations. Also, a chimney foundation probably will support a larger load than the adjacent
building foundations. For this reason, chimney footings
and foundations are often separated from the building
foundation. A chimney foundation monolithic with the
building foundation is permitted, provided the soil pressure and anticipated settlement are approximately uniform.
2113.3 Seismic reinforcing. Masonry or concrete chimneys
shall be constructed, anchored, supported and reinforced as required in this chapter. In Seismic Design Category D, masonry
and concrete chimneys shall be reinforced and anchored as detailed in Sections 2113.3.1, 2113.3.2 and 2113.4. In Seismic Design Category A, B or C, reinforcement and seismic anchorage
is not required. In Seismic Design Category E or F, masonry and
concrete chimneys shall be reinforced in accordance with the requirements of Sections 2101 through 2108.
v Unreinforced fireplaces and chimneys subjected to
strong ground motion have been severely damaged in
past earthquakes. The requirements in this section provide minimum reinforcement in an effort to keep these
structures together during such events. More substantial reinforcement, however, may be required in areas of
high seismicity or for atypical chimneys.
2113.3.1 Vertical reinforcing. For chimneys up to 40 inches
(1016 mm) wide, four No. 4 continuous vertical bars anchored
in the foundation shall be placed in the concrete, between
wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103.10. Grout
shall be prevented from bonding with the flue liner so that the
flue liner is free to move with thermal expansion. For chimneys
greater than 40 inches (1016 mm) wide, two additional No. 4
vertical bars shall be provided for each additional 40 inches
(1016 mm) in width or fraction thereof.
v These requirements are traditional minimum prescriptive provisions to help maintain the structural integrity of
fireplaces and chimneys during earthquakes. More reinforcement may be required in areas of high seismicity or
for atypical chimneys.
21-69
2113.3.2 – 2113.7
2113.3.2 Horizontal reinforcing. Vertical reinforcement shall
be placed enclosed within 1/4-inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) o.c. in concrete, or placed in the bed
joints of unit masonry, at a minimum of every 18 inches (457
mm) of vertical height. Two such ties shall be provided at each
bend in the vertical bars.
v These requirements are traditional minimum prescriptive provisions intended to help maintain the integrity of
fireplaces and chimneys during earthquakes. The vertical reinforcement required by Section 2113.3.1 must be
enclosed within the horizontal reinforcement required
by this section. More reinforcement may be required in
areas of high seismicity or for atypical chimneys.
2113.4 Seismic anchorage. Masonry and concrete chimneys
and foundations in Seismic Design Category D shall be anchored at each floor, ceiling or roof line more than 6 feet (1829
mm) above grade, except where constructed completely within
the exterior walls. Anchorage shall conform to the following requirements.
v Fireplaces and chimneys must be connected to floor and
roof diaphragms to prevent overturning during earthquakes. Chimneys must be anchored at the ceiling line of
roof or ceiling assemblies and at floor levels below the
roof. Such anchorage is of lesser importance where the
floor assembly is 6 feet (1829 mm) or less above grade.
2113.4.1 Anchorage. Two 3/16-inch by 1-inch (4.8 mm by 25
mm) straps shall be embedded a minimum of 12 inches (305
mm) into the chimney. Straps shall be hooked around the outer
bars and extend 6 inches (152 mm) beyond the bend. Each strap
shall be fastened to a minimum of four floor joists with two
1
/2-inch (12.7 mm) bolts.
v The prescriptive requirements in this section are traditional for typical fireplaces and chimneys. More substantial anchorage may be required in areas of high
seismicity, for large fireplaces or where the distance between floor and roof diaphragms is large.
2113.5 Corbeling. Masonry chimneys shall not be corbeled
more than half of the chimney’s wall thickness from a wall or
foundation, nor shall a chimney be corbeled from a wall or foundation that is less than 12 inches (305 mm) in thickness unless it
projects equally on each side of the wall, except that on the second story of a two-story dwelling, corbeling of chimneys on the
exterior of the enclosing walls is permitted to equal the wall
thickness. The projection of a single course shall not exceed
one-half the unit height or one-third of the unit bed depth,
whichever is less.
v A corbel is formed by projecting courses of masonry
with the first or lowest course projecting out from the
face of the wall and each successive course projecting
out from the supporting course below. The angle of a
corbel is limited so that the structural capacities of the
masonry are not exceeded.
Figure 2113.5 illustrates the limitations of corbeling in
an eccentrically loaded masonry chimney. The total
21-70
MASONRY
corbeled projection cannot exceed 6 inches (152 mm).
Where corbeling projects from the wall on one side only,
the minimum allowable thickness of the wall is 12
inches (305 mm). The maximum allowable horizontal
projection of an individual course of brick cannot exceed
one-half the height and one-third the thickness of the
masonry unit.
A chimney that projects equally on each side of the
wall loads the wall concentrically. The requirement for a
minimum wall thickness of 12 inches (305 mm) does not
apply to this chimney configuration.
This section contains an exception to the limitations
on corbel projection. In single-family homes, traditional
chimneys originated in the second story and commonly
served heating appliances in bedrooms, studies and
sewing rooms. The exception allows corbeling to project from the exterior masonry wall a distance equivalent to the masonry wall thickness. This exception, however, does not affect the limitation on minimum wall
thickness stated in the second sentence of this section.
For example, a chimney in the second story of a
two-story building cannot be corbeled at all if the wall is
less than 12 inches (305 mm) thick and the corbeling is
to project from one side only. If the corbeling is to project
equally from both sides of the wall, the minimum wall
thickness does not apply.
2113.6 Changes in dimension. The chimney wall or chimney
flue lining shall not change in size or shape within 6 inches (152
mm) above or below where the chimney passes through floor
components, ceiling components or roof components.
v At changes in shape or direction, masonry chimneys
can have thinner walls, making them susceptible to
leakage of water from the outside and to hot spots and
leakage of combustion gases from the inside. This is a
fire hazard. The intent of this provision is to prohibit
changes in shape and size near combustible construction. This section prohibits any change in dimension or
direction of a masonry chimney from 6 inches (152 mm)
below the combustible construction to 6 inches (152
mm) above it (see Figure 2113.6).
2113.7 Offsets. Where a masonry chimney is constructed with a
fireclay flue liner surrounded by one wythe of masonry, the
maximum offset shall be such that the centerline of the flue
above the offset does not extend beyond the center of the chimney wall below the offset. Where the chimney offset is supported by masonry below the offset in an approved manner, the
maximum offset limitations shall not apply. Each individual
corbeled masonry course of the offset shall not exceed the projection limitations specified in Section 2113.5.
v An offset requires two changes in direction and causes
two vertical sections of a chimney to be offset (misaligned) from each other. The intent of this section is to
provide an upper portion of an offset that is structurally
stable with respect to the lower portion.
The offset limitation does not apply when the inclined
portion of the chimney and the portion above the offset
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2113.8 – 2113.9.1
are supported in an approved manner by underlying
masonry construction.
2113.8 Additional load. Chimneys shall not support loads other
than their own weight unless they are designed and constructed
to support the additional load. Masonry chimneys are permitted
to be constructed as part of the masonry walls or concrete walls
of the building.
v Because the requirements for chimneys in Section 2113
are based on past performance, chimneys should not
be used to support other loads unless they are specifically designed to do so.
COMBUSTIBLE FLOOR/
CEILING ASSEMBLY
2113.9 Termination. Chimneys shall extend at least 2 feet (610
mm) higher than any portion of the building within 10 feet (3048
mm), but shall not be less than 3 feet (914 mm) above the highest
point where the chimney passes through the roof.
6" MINIMUM
v Chimneys must be terminated well above adjacent portions of the building so that flue gases are exhausted
away from combustible materials and for proper airflow
through the chimney (see Figure 2113.9).
6" MINIMUM
COMBUSTIBLE
CONSTRUCTION
2113.9.1 Spark arrestors. Where a spark arrestor is installed on
a masonry chimney, the spark arrestor shall meet all of the following requirements:
1. The net free area of the arrestor shall not be less than four
times the net free area of the outlet of the chimney flue it
serves.
2. The arrestor screen shall have heat and corrosion resistance equivalent to 19-gage galvanized steel or 24-gage
stainless steel.
3. Openings shall not permit the passage of spheres having a
diameter greater than 1/2 inch (13 mm) nor block the pas-
NOT TO SCALE
For SI:
1 inch = 25.4 mm.
Figure 2113.6
MASONRY CHIMNEY CHANGE IN SHAPE (OFFSET)
H
D
MASONRY UNIT
MAX. 1/2 HEIGHT, H,
OF MASONRY UNIT
AND 1/3 DEPTH
OF MASONRY UNIT, D
12" MIN.
NOT MORE THAN
1/2 CHIMNEY WALL
THICKNESS
For SI: 1 inch = 25.4 mm.
Figure 2113.5
CORBELING LIMITATIONS
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-71
2113.10 – 2113.11.1.1
MASONRY
sage of spheres having a diameter less than 3/8 inch (11
mm).
struction of the chimney walls and allows the chimney to
be gas tight.
4. The spark arrestor shall be accessible for cleaning and the
screen or chimney cap shall be removable to allow for
cleaning of the chimney flue.
2113.11.1 Residential-type appliances (general). Flue lining
systems shall comply with one of the following:
1. Clay flue lining complying with the requirements of
ASTM C 315, or equivalent.
2. Listed chimney lining systems complying with UL 1777.
3. Factory-built chimneys or chimney units listed for installation within masonry chimneys.
4. Other approved materials that will resist corrosion, erosion, softening or cracking from flue gases and condensate at temperatures up to 1,800°F (982°C).
v This section provides specifications for spark arrestors,
if they are provided. Their use is not mandated by the
code, but owners or builders often install them.
2113.10 Wall thickness. Masonry chimney walls shall be constructed of concrete, solid masonry units or hollow masonry
units grouted solid with not less than 4 inches (102 mm) nominal thickness.
v The minimum chimney wall thickness is necessary to
achieve a thermal mass that will predictably control heat
transmission through the walls of the chimney.
2113.11 Flue lining (material). Masonry chimneys shall be
lined. The lining material shall be appropriate for the type of appliance connected, according to the terms of the appliance listing and the manufacturer’s instructions.
v The liner forms the flue passageway and is the actual
conduit for all products of combustion. The flue lining is
required to withstand exposure to high temperatures
and corrosive chemicals. It protects the masonry con-
v This section requires that the lining for residential-type
appliances comply with ASTM C 315 or other approved
equivalent and be capable of resisting degradation from
flue gas. Chimney liner systems that are tested and labeled by an approved agency in accordance with UL
1777 are also permitted.
2113.11.1.1 Flue linings for specific appliances. Flue linings
other than those covered in Section 2113.11.1 intended for use
with specific appliances shall comply with Sections 2113.11.1.2
through 2113.11.1.4 and Sections 2113.11.2 and 2113.11.3.
v This section identifies flue lining materials to be used for
specific appliances.
<10'-0"
2'-0" MIN.
RIDGE
3'-0" MIN.
CROSS SECTION - WHEN 10'-0" OR LESS FROM RIDGE
>10'-0"
10'-0"
2'-0" MIN.
RIDGE
3'-0" MIN.
HIGHEST POINT
OF THE ROOF
THAT IS WITHIN
10'-0" OF THE CHIMNEY
CROSS SECTION - WHEN MORE THAN 10'-0" FROM RIDGE
For SI: 1 foot = 304.8 mm.
Figure 2113.9
MINIMUM TERMINATION OF CHIMNEYS
21-72
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2113.11.1.2 Gas appliances. Flue lining systems for gas appliances shall be in accordance with the International Fuel Gas
Code.
v The International Fuel Gas Code® (IFGC®) must be
used to determine appropriate flue-lining systems for
gas appliances.
2113.11.1.3 Pellet fuel-burning appliances. Flue lining and
vent systems for use in masonry chimneys with pellet fuel-burning appliances shall be limited to flue lining systems complying
with Section 2113.11.1 and pellet vents listed for installation
within masonry chimneys (see Section 2113.11.1.5 for marking).
v Flue-lining and vent systems in masonry chimneys of
pellet fuel-burning appliances can either conform to
Section 2113.11.1 or be an approved listed system.
2113.11.1.4 Oil-fired appliances approved for use with
L-vent. Flue lining and vent systems for use in masonry chimneys with oil-fired appliances approved for use with Type L vent
shall be limited to flue lining systems complying with Section
2113.11.1 and listed chimney liners complying with UL 641
(see Section 2113.11.1.5 for marking).
v Flue lining and vent systems in masonry chimneys of
oil-fired appliances with Type L vents can either conform to Section 2113.11.1 or be an approved listed system (UL 641).
2113.11.1.5 Notice of usage. When a flue is relined with a material not complying with Section 2113.11.1, the chimney shall be
plainly and permanently identified by a label attached to a wall,
ceiling or other conspicuous location adjacent to where the connector enters the chimney. The label shall include the following
message or equivalent language: “This chimney is for use only
with (type or category of appliance) that burns (type of fuel). Do
not connect other types of appliances.”
v Clearly displayed information on the appropriate use
and fuel for appliances is required to protect against the
use of improper types of fuel that could cause fire.
2113.11.2 Concrete and masonry chimneys for medium-heat
appliances.
v This section establishes requirements for masonry
chimneys serving medium-heat appliances, including
the chimney materials, lining, termination height and
proper clearances to combustibles.
2113.11.2.1 General. Concrete and masonry chimneys for medium-heat appliances shall comply with Sections 2113.1
through 2113.5.
v Chimneys serving a medium-heat appliance must comply with the general chimney requirements in Sections
2113.1 through 2113.5. These include minimum requirements for footings and foundations; seismic
reinforcement; anchorage and corbeling.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
2113.11.1.2 – 2113.11.2.4
2113.11.2.2 Construction. Chimneys for medium-heat appliances shall be constructed of solid masonry units or of concrete
with walls a minimum of 8 inches (203 mm) thick, or with stone
masonry a minimum of 12 inches (305 mm) thick.
v Masonry chimneys for medium-heat appliances must
be constructed of concrete in accordance with Chapter
19, or of solid masonry units in accordance with this
chapter. Chimneys constructed of solid masonry units
or reinforced concrete are required to have a minimum
wall thickness of 8 inches (203 mm). The minimum
thickness requirement is necessary to achieve a thermal mass that will predictably control heat transmission
through the walls of the chimney. Chimneys constructed
of rubble stone masonry (irregular or roughly shaped
stones) are required to have a wall thickness of no less
than 12 inches (305 mm). The rate of heat transmission
through stone walls is not predictable because of the
varying thickness of the individual stones and the nonuniform mortar joints between the stones. For these
reasons, stone wall chimneys are required to be thicker
to provide a reasonable margin of safety.
2113.11.2.3 Lining. Concrete and masonry chimneys shall be
lined with an approved medium-duty refractory brick a minimum of 41/2 inches (114 mm) thick laid on the 41/2-inch bed (114
mm) in an approved medium-duty refractory mortar. The lining
shall start 2 feet (610 mm) or more below the lowest chimney
connector entrance. Chimneys terminating 25 feet (7620 mm) or
less above a chimney connector entrance shall be lined to the
top.
v A medium-heat appliance produces flue gas temperatures up to 2,000°F (1093°C). The chimney lining reduces heat transmission to the walls of the chimney and
contains flue gases within a continuous duct until they
are away from the building. This section requires at
least a medium-duty refractory brick. A 41/2-inch (114
mm) medium-duty refractory brick lining tested and
classified in accordance with ASTM C 27 meets this criterion. Each course of the refractory brick liner is required to be installed on a full bed of refractory mortar to
form a structurally stable, continuous, gas-tight liner.
Figure 2113.11.2.3 depicts a masonry chimney serving a medium-heat appliance. The liner extends from 2
feet (610 mm) below the lowest inlet to the top of the
chimney, which is located less than 25 feet (7620 mm)
above the highest inlet.
A chimney liner is required in all portions of the chimney that are exposed to flue gases. The liner is required
to extend below the lowest inlet to provide protection to
the masonry from flue gases, which can deteriorate the
masonry and the mortar joints.
2113.11.2.4 Multiple passageway. Concrete and masonry
chimneys containing more than one passageway shall have the
liners separated by a minimum 4-inch-thick (102 mm) concrete
or solid masonry wall.
v When a chimney requires multiple passageways, a
4-inch (102 mm) partition of solid masonry is required
21-73
2113.11.2.5 – 2113.11.3.2
MASONRY
between them to act as a barrier between passageways
and to enhance structural integrity.
2113.11.2.5 Termination height. Concrete and masonry chimneys for medium-heat appliances shall extend a minimum of 10
feet (3048 mm) higher than any portion of any building within
25 feet (7620 mm).
v Chimneys for medium-heat appliances are required to
extend at least 10 feet (3048 mm) above the highest
portion of the building within 25 feet (7620 mm) horizontally. This is intended to provide an acceptable height to
carry away the flue gases safely and to provide adequate clearance to the roof and surrounding structures
to allow any burning embers to extinguish before
landing.
2113.11.3 Concrete and masonry chimneys for high-heat appliances.
v This section establishes the requirements for concrete
and masonry chimneys serving high-heat appliances,
including chimney materials, lining, termination height
and proper clearances to combustibles.
2113.11.3.1 General. Concrete and masonry chimneys for
high-heat appliances shall comply with Sections 2113.1 through
2113.5.
v Chimneys serving high-heat appliances are required to
comply with the general chimney requirements in Sections 2113.1 through 2113.5, including minimum provisions for footings and foundations; seismic reinforcement; anchorage and corbeling.
2113.11.2.6 Clearance. A minimum clearance of 4 inches (102
mm) shall be provided between the exterior surfaces of a concrete or masonry chimney for medium-heat appliances and
combustible material.
2113.11.3.2 Construction. Chimneys for high-heat appliances
shall be constructed with double walls of solid masonry units or
of concrete, each wall to be a minimum of 8 inches (203 mm)
thick with a minimum airspace of 2 inches (51 mm) between the
walls.
v A 4-inch (102 mm) minimum airspace clearance to combustibles is required for a medium-heat masonry chimney.
This large clearance is needed because of the higher temperatures produced by medium-heat appliances.
v The flue gases produced by a high-heat appliance can
have temperatures above 2,000°F (1,093°C). To prevent fire, such chimneys must be enclosed by two
wythes of masonry with an airspace between them.
WHEN DISTANCE IS LESS THAN
25'-0", LINER IS REQUIRED
TO EXTEND TO TOP OF CHIMNEY
10'-0" MINIMUM ABOVE
ANY PORTION OF BUILDING
WITHIN 25'-0"
APPLIANCE FLUE CONNECTION
2'-0" MIN. BELOW
LOWEST CHIMNEY
INLET
CLEANOUT
For
SI: 1 foot = 304.8 mm.
Figure 2113.11.2.3
MASONRY CHIMNEY FOR MEDIUM-HEAT APPLIANCE
21-74
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
Thus, the chimney liner is required to be protected by
two solid masonry unit walls or reinforced concrete
walls, each a minimum of 8 inches (204 mm) thick with
an airspace between them of at least 2 inches (51 mm).
The airspace is intended to provide thermal insulation
and to allow for thermal expansion of the chimney
components.
2113.11.3.3 Lining. The inside of the interior wall shall be lined
with an approved high-duty refractory brick, a minimum of 41/2
inches (114 mm) thick laid on the 41/2-inch bed (114 mm) in an
approved high-duty refractory mortar. The lining shall start at
the base of the chimney and extend continuously to the top.
2113.11.3.3 – 2113.14
Fireclay flue liners shall be laid in medium-duty refractory
mortar conforming to ASTM C 199, with tight mortar joints left
smooth on the inside and installed to maintain an airspace or insulation not to exceed the thickness of the flue liner separating the
flue liners from the interior face of the chimney masonry walls.
Flue lining shall be supported on all sides. Only enough mortar
shall be placed to make the joint and hold the liners in position.
v The liner forms the flue passageway and is the actual
conduit of all products of combustion. It must withstand
exposure to high temperatures and corrosive chemicals
from the flue gases. The chimney lining protects the masonry construction of the chimney walls and allows the
chimney to be constructed gas tight.
Installation must comply with ASTM C 1283. The liner
is required to extend below the lowest inlet to provide
protection to the masonry from flue gases, which can
deteriorate the masonry and mortar joints.
Refractory mortar must comply with ASTM C 199.
v High-heat appliances can produce flue gases with temperatures exceeding 2,000°F (1,093°C). The chimney
lining reduces heat transmission to the walls of the
chimney and contains flue gases within a continuous
passageway until they are outside the building. This
section permits only a high-duty refractory brick having
a minimum thickness of 41/2 inches (114 mm) to be used
in a masonry chimney serving a high-heat appliance. An
approved high-duty refractory lining usually consists of
brick tested and classified in accordance with ASTM C
27. To provide a structurally stable and continuous
gas-tight liner, each course of the refractory brick liner
must be laid on a full bed of refractory mortar approved
for high-heat appliances.
2113.13.1 Listed materials. Listed materials used as flue linings shall be installed in accordance with the terms of their listings and the manufacturer’s instructions.
2113.11.3.4 Termination height. Concrete and masonry chimneys for high-heat appliances shall extend a minimum of 20 feet
(6096 mm) higher than any portion of any building within 50
feet (15 240 mm).
v Listed materials for flue linings must be installed in accordance with the manufacturer’s instructions. Such instructions are not listed in the code since they vary with
each system.
2113.13 Additional requirements.
v This section contains requirements for listed materials
to be used as flue linings and for spaces surrounding
chimney lining systems.
v Chimneys for high-heat appliances must terminate at
least 20 feet (6096 mm) above the highest portion of the
building within 50 feet (15 240 mm) horizontally. This allows flue gases to be safely carried away and provides
enough clearance to allow any burning embers to extinguish before landing on combustibles.
2113.13.2 Space around lining. The space surrounding a chimney lining system or vent installed within a masonry chimney
shall not be used to vent any other appliance.
2113.11.3.5 Clearance. Concrete and masonry chimneys for
high-heat appliances shall have approved clearance from buildings and structures to prevent overheating combustible materials, permit inspection and maintenance operations on the
chimney and prevent danger of burns to persons.
v The space surrounding a chimney lining system provides
a thermal buffer between the flue and the surrounding masonry. Using it for another purpose is prohibited.
v The extremely high-temperature flue gas produced by a
high-heat appliance is a major fire safety concern and
requiring sufficient clearance from buildings protects
nearby combustible material, permits inspection and
maintenance of the chimney and minimizes danger to
persons.
2113.12 Flue lining (installation). Flue liners shall be installed
in accordance with ASTM C 1283 and extend from a point not
less than 8 inches (203 mm) below the lowest inlet or, in the case
of fireplaces, from the top of the smoke chamber, to a point
above the enclosing walls. The lining shall be carried up vertically, with a maximum slope no greater than 30 degrees (0.52
rad) from the vertical.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
Exception: This shall not prevent the installation of a separate flue lining in accordance with the manufacturer’s instructions.
2113.14 Multiple flues. When two or more flues are located in
the same chimney, masonry wythes shall be built between adjacent flue linings. The masonry wythes shall be at least 4 inches
(102 mm) thick and bonded into the walls of the chimney.
Exception: When venting only one appliance, two flues are
permitted to adjoin each other in the same chimney with only
the flue lining separation between them. The joints of the adjacent flue linings shall be staggered at least 4 inches (102
mm).
v A single masonry chimney can contain any number of
flue-gas passageways. When more than two flues are
contained in the same chimney, the flue liners are required to be subdivided by masonry wythes into groups
of not more than two (see Figure 2113.14). The purpose
of the masonry wythes is to unify the chimney structur21-75
2113.15 – 2113.16
MASONRY
ally and to isolate pairs of flues serving dissimilar
appliances.
2113.15 Flue area (appliance). Chimney flues shall not be
smaller in area than the area of the connector from the appliance.
Chimney flues connected to more than one appliance shall not
be less than the area of the largest connector plus 50 percent of
the areas of additional chimney connectors.
Exceptions:
1. Chimney flues serving oil-fired appliances sized in accordance with NFPA 31.
2. Chimney flues serving gas-fired appliances sized in
accordance with the International Fuel Gas Code.
v Flues are sized to match the opening at the top of the
appliance so that appliances function properly. Smaller
flues are not permitted since they may constrict the passage of gases out from the appliance. The International
Residential Code® (IRC®) provides guidelines on the
sizing of these flues.
2113.16 Flue area (masonry fireplace). Flue sizing for chimneys serving fireplaces shall be in accordance with Section
2113.16.1 or 2113.16.2.
v This section provides requirements for the net
cross-sectional area of the flue and throat between the
firebox and the smoke chamber. Airflow through the fire-
place is affected by the dimensions of the firebox opening, the shape and cross-sectional area of the flue and
the height of the chimney (see Code Figure 2113.16).
For proper fireplace operation, the required cross-sectional area is about one-tenth that of the fireplace opening. This ratio may vary somewhat with the height of the
chimney and the configuration (round or rectangular) of
the chimney flue.
Section 2113.16.1 prescribes the minimum flue area
based on the fireplace opening alone, while Section
2113.16.2 prescribes it based on the height of the fireplace, the fireplace opening area and flue type.
FIGURE 2113.16. See page 21-77.
v This figure prescribes minimum flue sizes as a function
of chimney height and the fireplace opening area. For
example, for a 20-foot-high (6096 mm) chimney and a
fireplace opening area of 2,000 square inches (1 290
320 mm2), the minimum cross-sectional area is 205 1/2
square inches (132 548 mm2) for a round flue or 241 1/2
square inches (155 767 mm2) for a square or rectangular flue. Using Table 2113.16 (1), that minimum required
cross-sectional area can be met by a circular flue with a
diameter of 18 inches (457 mm). Using Table
2113.16(2), the minimum cross-sectional area would require a square flue with an inside dimension of 19 1/2
inches (495 mm).
MIN. 4" SOLID MASONRY
PLAN
STAGGER JOINTS OF
ADJOINING FLUE LINERS
A MIN. OF 4"
SECTION
For SI:
1 inch = 25.4 mm.
Figure 2113.14
LOW-HEAT CHIMNEY WITH MORE THAN TWO FLUES
21-76
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2113.16.1 – 2113.16.2
2113.16.1 Minimum area. Round chimney flues shall have a
minimum net cross-sectional area of at least 1/12 of the fireplace
opening. Square chimney flues shall have a minimum net
cross-sectional area of at least 1/10 of the fireplace opening. Rectangular chimney flues with an aspect ratio less than 2 to 1 shall
have a minimum net cross-sectional area of at least 1/10 of the
fireplace opening. Rectangular chimney flues with an aspect ratio of 2 to 1 or more shall have a minimum net cross-sectional
area of at least 1/8 of the fireplace opening.
v This section prescribes the minimum flue area based on
the fireplace opening and the shape of the flue. For a
given size fireplace, circular chimney flues are permitted to have a smaller area than rectangular flues. Wide,
narrow flues require a larger area for adequate airflow.
For SI:
2113.16.2 Determination of minimum area. The minimum
net cross-sectional area of the flue shall be determined in accordance with Figure 2113.16. A flue size providing at least the
equivalent net cross-sectional area shall be used. Cross-sectional areas of clay flue linings are as provided in Tables
2113.16(1) and 2113.16(2) or as provided by the manufacturer
or as measured in the field. The height of the chimney shall be
measured from the firebox floor to the top of the chimney flue.
v This section provides an alternate method to determine
flue size based on the height of the chimney, the fireplace opening area and the flue type [see commentary,
Tables 2113.16(1) and 2113.16(2) and Code Figure
2113.16].
1 inch = 25.4 mm, 1 square inch = 645 mm2.
FIGURE 2113.16
FLUE SIZES FOR MASONRY CHIMNEYS
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-77
TABLE 2113.16(1) – 2113.19
MASONRY
TABLE 2113.16(1)
NET CROSS-SECTIONAL AREA OF ROUND FLUE SIZESa
FLUE SIZE, INSIDE DIAMETER
(inches)
CROSS-SECTIONAL AREA
(square inches)
6
28
7
38
8
50
10
78
3
10 /4
90
12
113
15
176
18
254
For SI: 1 inch = 25.4 mm, 1 square inch = 645.16
a. Flue sizes are based on ASTM C 315.
mm2.
v This table gives the areas of circular flues of standard
sizes so that users of the code can easily determine a
flue size complying with Code Figure 2113.16. The flue
areas shown in this table are determined by the equation A = B x (d/2)2, where A is the cross-sectional area, d
is the inside diameter of the flue and B is approximated
as 3.14. Alternately, a minimum diameter can be calculated as d = [(A/B)½]/4.
TABLE 2113.16(2)
NET CROSS-SECTIONAL AREA OF SQUARE AND
RECTANGULAR FLUE SIZESa
FLUE SIZE, INSIDE DIMENSION
(inches)
CROSS-SECTIONAL AREA
(square inches)
41/2 × 13
34
71/
2
37
8 / 2 × 8 /2
47
1
7 /2 × 11 /2
58
× 13
74
71/
2×
1
1
1
8 1/
2
71/2 × 151/2
82
11 /2 × 11 /2
91
1
/2 × 17 /2
101
13 × 13
122
1
81
1
111/
2
×
151/
124
2
13 × 17 /2
1
151
165
/2 × 15 /2
151/
1
×
191/
168
2
214
17 /2 × 17 /2
226
19 /2 × 19 /2
269
2
1
1
1
1
20 × 20
For SI: 1 inch = 25.4 mm, 1 square inch = 645.16
a. Flue sizes are based on ASTM C 315.
286
mm2.
v This table gives the area of square and rectangular
flues of standard sizes so that code users can easily de21-78
termine a flue size complying with Code Figure 2113.16.
Because the flue corners are rounded, the flue areas
shown in this table are not determined by simply multiplying the inside dimensions shown. The areas are accordingly slightly smaller than a true rectangle of the dimensions shown in the table.
2113.17 Inlet. Inlets to masonry chimneys shall enter from the
side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of
the inlet or from extending beyond the wall of the liner.
v The inlet must be noncombustible and strong enough
not to be pulled out.
2113.18 Masonry chimney cleanout openings. Cleanout
openings shall be provided within 6 inches (152 mm) of the base
of each flue within every masonry chimney. The upper edge of
the cleanout shall be located at least 6 inches (152 mm) below
the lowest chimney inlet opening. The height of the opening
shall be at least 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.
Exception: Chimney flues serving masonry fireplaces,
where cleaning is possible through the fireplace opening.
v This section requires a cleanout to be installed in a chimney to facilitate cleaning and inspection. A fireplace inherently provides access to its chimney through the firebox,
throat and smoke chamber. The cleanout cover and opening frame are to be of an approved noncombustible material, such as cast iron or precast concrete and must be arranged to remain tightly closed. The requirement for
placing the cleanout at least 6 inches (152 mm) below the
lowest connection to the chimney is intended to minimize
the possibility of combustion products exiting the chimney
through the cleanout.
2113.19 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior
wall of the building shall have a minimum airspace clearance to
combustibles of 2 inches (51 mm). Chimneys located entirely
outside the exterior walls of the building, including chimneys
that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be
filled, except to provide fireblocking in accordance with Section
2113.20.
Exceptions:
1. Masonry chimneys equipped with a chimney lining
system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777,
and installed in accordance with the manufacturer’s instructions, are permitted to have combustible material
in contact with their exterior surfaces.
2. Where masonry chimneys are constructed as part of
masonry or concrete walls, combustible materials shall
not be in contact with the masonry or concrete wall less
than 12 inches (305 mm) from the inside surface of the
nearest flue lining.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
2113.20
3. Exposed combustible trim and the edges of sheathing
materials, such as wood siding, are permitted to abut
the masonry chimney sidewalls, in accordance with
Figure 2113.19, provided such combustible trim or
sheathing is a minimum of 12 inches (305 mm) from
the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of
the chimney by more than 1 inch (25 mm).
v Clearance between the external surfaces of the masonry chimney and all combustible materials must be
maintained. The intent of this section is to require a
2-inch (51 mm) minimum airspace clearance between
combustibles and surfaces of all chimneys located in
the interior of a building or within an exterior wall assembly. A 1-inch (25 mm) airspace clearance is allowed only
where the chimney is located entirely outside of the
building.
If any portion of a chimney is located in an exterior wall,
that chimney must be considered as an interior chimney
and must have a 2-inch (51 mm) minimum airspace clearance. The 1-inch (25 mm) clearance is allowed because
the exterior surface of an outdoor chimney can dissipate
heat. An outdoor chimney is exposed to outdoor ambient
temperatures, allowing it to operate with cooler surface
temperatures. Like all airspace clearances, the 1-inch (25
mm) airspace clearance is not permitted to be filled with
any material except the noncombustible material necessary for fireblocking. The required clearance for exterior
chimneys applies to all combustible materials, including
sheathing, siding, insulation, framing and trim.
The exception recognizes a variety of chimney liners
that are tested and labeled in accordance with UL 1777.
UL 1777 covers metallic and nonmetallic chimney liners
intended for field installation into new and existing masonry
chimneys used for natural draft venting of gas, oil and
solid-fuel-burning appliances having maximum continuous
flue-gas temperatures not exceeding 1,000°F (538°C).
Some lining systems are labeled for reduced clearance applications and could allow the construction or rehabilitation of
chimneys in contact with combustibles, without compromising the safety normally provided by the code-prescribed airspace clearances.
Chimney liner systems are typically metal or
poured-in-place concrete and incorporate insulation to retard
the transfer of heat to the surrounding masonry walls of the
chimney.
FIGURE 2113.19. See below.
v This figure clarifies Exception 3 to the clearance requirements for masonry chimneys. The edge abutment
of combustible sheathing or trim where there is an adequate thickness of masonry is a long-standing practice
that is considered safe, provided the minimum clearance to the flue lining is maintained.
2113.20 Chimney fireblocking. All spaces between chimneys
and floors and ceilings through which chimneys pass shall be
fireblocked with noncombustible material securely fastened in
place. The fireblocking of spaces between wood joists, beams or
headers shall be to a depth of 1 inch (25 mm) and shall only be
placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.
v Fireblocking is required to prevent the travel of flames,
smoke and hot gases to other areas of the building
through the gaps between the chimney and the floor or
ceiling assemblies. The 1-inch (25 mm) depth requirement is intended to be both the minimum and the maximum [see Figures 2113.20(1) and (2)].
For SI: 1 inch = 25.4 mm
FIGURE 2113.19
ILLUSTRATION OF EXCEPTION TO
CHIMNEY CLEARANCE PROVISION
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
21-79
FIGURE 2113.20(1) – FIGURE 2113.20(2)
MASONRY
NONCOMBUSTIBLE FIREBLOCK
Figure 2113.20(1)
FIREBLOCKING
2"
COMBUSTIBLE
FRAMING
2"
1"-THICK NONCOMBUSTIBLE
FIREBLOCKING HELD IN PLACE
WITH METAL STRIPS OR LATH
For SI:
1 inch = 25.4 mm.
Figure 2113.20(2)
FIREBLOCKING (SECTION)
21-80
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
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Conshohocken, PA: ASTM International, 1987.
ASTM C 199-84 (2000), Standard Test Method for Pier
Test for Refractory Mortars. West Conshohocken, PA:
ASTM International, 2000.
ASTM C 207-97, Standard Specification for Hydrated
Lime for Masonry Purposes. West Conshohocken, PA:
ASTM International, 1997.
ASTM C 212-00, Specification for Structural Clay Facing
Tile. West Conshohocken, PA: ASTM International,
2000.
ASTM C 216-01A, Specification for Facing Brick (Solid
Masonry Units Made from Clay or Shale). West
Conshohocken, PA: ASTM International, 2001.
ASTM C 217-01A, Standard Test Method for Weather Resistance of Natural Slate. West Conshohocken, PA:
ASTM International, 2001.
ASTM C 270-01A, Specification for Mortar for Unit Masonry. West Conshohocken, PA: ASTM International,
2001.
ASTM C 305-82, Standard Method for Mechanical Mixing
of Hydraulic Cement Pastes and Mortars for Plastic
Consistency. West Conshohocken, PA: ASTM International, 1982.
ASTM C 315-00, Specification for Clay Flue Linings. West
Conshohocken, PA: ASTM International, 2000.
ASTM C 331-01, Standard Specification for Lightweight
Aggregates for Concrete Masonry Units. West
Conshohocken, PA: ASTM International, 2001.
ASTM C 404-87, Standard Specification for Aggregates
for Masonry Grout. West Conshohocken, PA: ASTM International, 1987.
ASTM C 476-01, Specification for Grout for Masonry.
West Conshohocken, PA: ASTM International, 2001.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
MASONRY
ASTM C 503-99eo1, Specification For Marble Dimension
Stone (Exterior). West Conshohocken, PA: ASTM International, 1999.
ASTM E 119-00, Test Methods for Fire Tests of Building
Construction and Materials. West Conshohocken, PA:
ASTM International, 2000.
ASTM C 568-99, Specification for Limestone Dimension
Stone. West Conshohocken, PA: ASTM International,
1999.
ASTM E 447-92b, Tests Methods for Compressive
Strength of Masonry Prisms. West Conshohocken, PA:
ASTM International, 1992.
ASTM C 595-00, Specification for Blended Hydraulic Cements. West Conshohocken, PA: ASTM International,
2000.
ASTM C 615-99, Specification for Granite Dimension
Stone. West Conshohocken, PA: ASTM International,
1999.
ASTM C 616-99, Specification for Quartz-Based Dimension Stone. West Conshohocken, PA: ASTM International, 1999.
ASTM C 629-99, Specification for Slate Dimension Stone.
West Conshohocken, PA: ASTM International, 1999.
ASTM C 652-01A, Specification for Hollow Brick (Hollow
Masonry Units Made from Clay or Shale). West
Conshohocken, PA: ASTM International, 2001.
ASTM C 744-99, Specification for Prefaced Concrete and
Calcium Silicate Masonry Units. West Conshohocken,
PA: ASTM International, 1999.
ASTM E 1602-01, Standard Guide for Construction of
Solid Fuel Burning Masonry Heaters. West
Conshohocken, PA: ASTM International, 2001.
AWS D 1.4-98, Structural Welding Code—Reinforced
Steel. Miami, FL: American Welding Society, 1998.
Baker, Ira. A Treatise on Masonry Construction. Chicago:
University of Illinois, 1889.
Commentary on Building Code Requirements for Masonry
Structures (ACI 530-02/ASCE 5-02/TMS 402-02).
Farmington Hills, MI: American Concrete Institute;
Reston, VA: Structural Engineering Institute of the
American Society of Civil Engineers; Boulder, CO: The
Masonry Society, 2002.
ASTM C 887-01, Specification for Packaged, Dry, Combined Materials for Surface Bonding Mortar. West
Conshohocken, PA: ASTM International, 2001.
Commentary on Specifications for Masonry Structures
(ACI 530.1-02/ASCE 6-02/TMS 602-02). Farmington
Hills, MI: American Concrete Institute; Reston, VA:
Structural Engineering Institute of the American Society of Civil Engineers; Boulder, CO: The Masonry Society, 2002.
ASTM C 946-91 (2001), Practice for Construction of
Dry-Stacked,
Surface-Bonded
Walls.
West
Conshohocken, PA: ASTM International, 2001.
Compressive Strength Testing of Masonry Mortar, A TMS
Monograph. Boulder, CO: The Masonry Society, 1996.
ASTM C 1019-00B (1993), Test Method for Sampling and
Testing Grout. West Conshohocken, PA: ASTM International, 2000.
IFC-03, International Fire Code. Falls Church, VA: International Code Council, 2003.
ASTM C 1088-01A, Specification for Thin Veneer Brick
Units Made from Clay or Shale. West Conshohocken,
PA: ASTM International, 2001.
IFGC-03, International Fuel Gas Code. Falls Church, VA:
International Code Council, 2003.
ASTM C 1261-98, Firebox Brick for Residential Fireplaces. West Conshohocken, PA: ASTM International,
1998.
ASTM C 1283-00, Standard Practice for Installing Clay
Flue Liners. West Conshohocken, PA: ASTM International, 2000.
ASTM C 1314-02, Standard Method for Constructing and
Testing Masonry Prisms Used to Determine Compliance with Specified Compressive Strength of Masonry.
West Conshohocken, PA: ASTM International, 2002.
ASTM C 1327-97, Specification for Mortar Cement. West
Conshohocken, PA: ASTM International, 1997.
ASTM E 84-01, Test Method for Surface Burning Characteristics of Building Materials. West Conshohocken,
PA: ASTM International, 2001.
2003 INTERNATIONAL BUILDING CODE® COMMENTARY
IRC-03, International Residential Code. Falls Church, VA:
International Code Council, 2003.
NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures. Washington, DC: Building Seismic Safety Council, 1997.
Standard Building Code©. Birmingham, AL: Southern
Building Code Congress International, Inc., 1997.
UL 641-95. Type L Low-Temperature Venting Systems.
Northbrook, IL: Underwriters Laboratories Inc., 1995.
UL 1777-98, Chimney Liners. Northbrook, IL: Underwriters Laboratories Inc., 1998.
Uniform Building Code™. Whittier, CA: International Conference of Building Officials, 1997.
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2003 INTERNATIONAL BUILDING CODE® COMMENTARY